arch/xtensa/esp32: Add support for RTC IRQs

[lucasssvaz]

Summary

Separate from GPIOs and add a handler for RTC interrupts.
Also replaces the RTC watchdog interrupt handler with the new one.

Impact

None on existing features. Add support for handling interruptions from RTC peripherals.

Testing

Tested using the watchdog example on the ESP32-DevKitC. (watchdog2 is the RTC one)

NuttShell (NSH) NuttX-10.4.0
nsh> wdog -i /dev/watchdog2
  ping elapsed=0
  ping elapsed=500
  ping elapsed=1000
  ping elapsed=1500
  ping elapsed=2000
  ping elapsed=2500
  ping elapsed=3000
  ping elapsed=3500
  ping elapsed=4000
  ping elapsed=4500
  NO ping elapsed=5000
  NO ping elapsed=5500
  NO ping elapsed=6000
ets Jul 29 2019 12:21:46

rst:0x10 (RTCWDT_RTC_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:6640
load:0x40078000,len:14848
load:0x40080400,len:3672
entry 0x4008068c
I (28) boot: ESP-IDF v4.4.2 2nd stage bootloader
I (28) boot: compile time 14:59:14
I (28) boot: chip revision: 3
I (30) boot_comm: chip revision: 3, min. bootloader chip revision: 0
I (38) boot.esp32: SPI Speed      : 40MHz
I (42) boot.esp32: SPI Mode       : DIO
I (47) boot.esp32: SPI Flash Size : 4MB
I (51) boot: Enabling RNG early entropy source...
I (57) boot: Partition Table:
I (60) boot: ## Label            Usage          Type ST Offset   Length
I (68) boot:  0 factory          factory app      00 00 00010000 00100000
I (75) boot: End of partition table
I (79) boot_comm: chip revision: 3, min. application chip revision: 0
I (86) esp_image: segment 0: paddr=00010020 vaddr=3f400020 size=027ech ( 10220) map
I (99) esp_image: segment 1: paddr=00012814 vaddr=3ffb1540 size=00220h (   544) load
I (103) esp_image: segment 2: paddr=00012a3c vaddr=40080000 size=01608h (  5640) load
I (114) esp_image: segment 3: paddr=0001404c vaddr=00000000 size=0bfcch ( 49100)
I (138) esp_image: segment 4: paddr=00020020 vaddr=400d0020 size=10c24h ( 68644) map
I (163) boot: Loaded app from partition at offset 0x10000
I (163) boot: Disabling RNG early entropy source...
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