ath25: 5.15: enable 5.15 testing kernel

ath25: 5.15: enable 5.15 testing kernel

Manually refreshed:
- 140-redboot_boardconfig.patch
- 141-redboot_partition_scan.patch
- 142-redboot_various_erase_size_fix.patch

Automatically refreshed:
- 107-ar5312_gpio.patch
- 108-ar2315_gpio.patch
- 110-ar2313_ethernet.patch
- 120-spiflash.patch
- 130-watchdog.patch
- 330-board_leds.patch

Use "make kernel_oldconfig" to refresh the new kernel config.

The Ubiquiti Nanostation 2 (XS2) and Ubiquiti Nanostation 5 (XS5) should
be marked as broken when switching to 5.15 by default. The new kernel
does not fit anymore into the partition.

Signed-off-by: Nick Hainke <vincent@systemli.org>