feat(mklittlefs): add command to format littlefs filesystems

Add an NSH command to format a device with littlefs, analogous to
mkfatfs for FAT filesystems. The command unmounts the mount point,
then remounts with forceformat to format and mount in one step.

Enable the command on boards that use littlefs as primary storage
(airbrainh743 and kakuteh7v2), and document it in the airbrainh743
flight controller page as a recovery procedure for a corrupted
flash filesystem.

Usage: mklittlefs /dev/mtd0 /fs/flash

docs/en/flight_controller/gearup_airbrainh743.md

@@ -91,6 +91,18 @@ Firmware can be installed in any of the normal ways:
 - [Load the firmware](../config/firmware.md) using _QGroundControl_.
   You can use either pre-built firmware or your own custom firmware.
 
+### Flash Storage Troubleshooting
+
+The AirBrainH743 uses a 128MB NAND flash (W25N) with a littlefs filesystem for [logging](../dev_log/logging.md).
+If the flash filesystem becomes corrupted, you can reformat it using the [System Console](../debug/system_console.md):
+
+```sh
+mklittlefs /dev/mtd0 /fs/flash
+```
+
+This will erase all data on the flash and create a fresh littlefs filesystem.
+The filesystem is immediately available after the command completes.
+
 ### System Console
 
 UART1 (ttyS0) is configured for use as the [System Console](../debug/system_console.md).

docs/en/releases/main.md

@@ -80,6 +80,7 @@ Please continue reading for [upgrade instructions](#upgrade-guide).
   - New [SDLOG_MAX_SIZE](../advanced_config/parameter_reference.md#SDLOG_MAX_SIZE) (default `1024` MB) caps the size of a single log file; once reached, the logger closes the current file and starts a new one.
   - New [SDLOG_ROTATE](../advanced_config/parameter_reference.md#SDLOG_ROTATE) (default `90`) sets the maximum disk usage percentage. Cleanup guarantees `(100 - SDLOG_ROTATE)%` of the disk stays free at all times, even while writing a new log file. Set `0` to disable space-based cleanup, `100` to allow filling the disk completely.
   - `SDLOG_DIRS_MAX` is now an orthogonal cap on the number of log directories (default `0` = disabled), on top of the space-based cleanup driven by `SDLOG_ROTATE` and `SDLOG_MAX_SIZE`. SITL defaults to `7`.
+- New `mklittlefs` systemcmd for reformatting a littlefs volume from the NSH console, analogous to `mkfatfs` for FAT filesystems.
 
 ### Ethernet