[SSCI824] Add rtos build

[toyowata]

• Add rtos TARGET_SSCI824 (same as LPC824) and test
• Fixed warning of pwmout_api.c by GCC_ARM

[toyowata]

automated test result is below:

Test summary:
+--------+---------+-----------+-------------+---------------------------------------+--------------------+---------------+-------+
| Result | Target  | Toolchain | Test ID     | Test Description                      | Elapsed Time (sec) | Timeout (sec) | Loops |
+--------+---------+-----------+-------------+---------------------------------------+--------------------+---------------+-------+
| OK     | SSCI824 | uARM      | DTCT_1      | Simple detect test                    |        0.47        |       10      |  1/1  |
| OK     | SSCI824 | uARM      | EXAMPLE_1   | /dev/null                             |        3.43        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_10     | Hello World                           |        0.38        |       5       |  1/1  |
| OK     | SSCI824 | uARM      | MBED_11     | Ticker Int                            |        11.4        |       15      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_12     | C++                                   |        1.42        |       10      |  1/1  |
| FAIL   | SSCI824 | uARM      | MBED_16     | RTC                                   |        4.52        |       20      |  0/1  |
| OK     | SSCI824 | uARM      | MBED_2      | stdio                                 |        0.75        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_23     | Ticker Int us                         |       11.42        |       15      |  1/1  |
| FAIL   | SSCI824 | uARM      | MBED_24     | Timeout Int us                        |       15.94        |       15      |  0/1  |
| OK     | SSCI824 | uARM      | MBED_25     | Time us                               |       11.72        |       15      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_26     | Integer constant division             |        1.42        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_34     | Ticker Two callbacks                  |        11.4        |       15      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_A1     | Basic                                 |        1.37        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_A21    | Call function before main (mbed_main) |        1.47        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_A9     | Serial Echo at 115200                 |        6.57        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | MBED_BUSOUT | BusOut                                |        2.32        |       15      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_1      | Basic thread                          |       11.37        |       15      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_2      | Mutex resource lock                   |       11.51        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_3      | Semaphore resource lock               |        8.52        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_4      | Signals messaging                     |        6.44        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_5      | Queue messaging                       |        2.43        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_6      | Mail messaging                        |        2.42        |       20      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_7      | Timer                                 |       11.34        |       15      |  1/1  |
| OK     | SSCI824 | uARM      | RTOS_8      | ISR (Queue)                           |        6.44        |       20      |  1/1  |
+--------+---------+-----------+-------------+---------------------------------------+--------------------+---------------+-------+
Result: 2 FAIL / 22 OK

Completed in 318.48 sec

[0xc0170]

@toyowata are you familiar why those 2 fail? (not relevant to this PR )

[toyowata]

RTC test (MBED_16) should only done for targets which support RTC (DEVICE_RTC defined by 1 in device.h). Need to modify tests.py.
I am not sure why we got a fail in the MBED_24. It sometime works, maybe timing problem?