boards/raspberrypi-4b: Add NXInit configuration

[linguini1]

Summary

This commit adds a configuration which uses the new "NXInit" to start up the board and the NSH shell. The init.rc file is pulled from the SD card, allowing users to create their own.

Impact

Configuration using the nxinit system! Users can now modify it as they need to
launch their own applications with nxinit.

Testing

Logs from config showing nxinit running before NSH on the Pi4B:

NuttShell (NSH) NuttX-12.13.0
nsh> ps
  TID   PID  PPID PRI POLICY   TYPE    NPX STATE    EVENT     SIGMASK            STACK    USED FILLED COMMAND
    0     0     0   0 FIFO     Kthread   - Ready              0000000000000000 0008144 0000928  11.3%  Idle_Task
    1     0     0 192 RR       Kthread   - Waiting  Semaphore 0000000000000000 0008080 0001088  13.4%  hpwork 0x48
    3     3     0 100 RR       Task      - Waiting  Semaphore 0000000000000000 0008112 0002880  35.5%  init_main
    4     4     3 100 RR       Task      - Running            0000000000000000 0008112 0003520  43.3%  nsh
nsh> ls
/:
 dev/
 proc/
 sd/

init.rc script used:

on boot
    start console
service console nsh
    class core
    restart_period 1000

[acassis]

Amazing!!!

[linguini1]

It's good to have some configs to test NXinit with! Sim would be a good target as well.

[acassis]

It's good to have some configs to test NXinit with! Sim would be a good target as well.

For sure! Maybe including more example showing all the features

[cederom]

Thank you @linguini1 :-)