pistachio: add 5.15 testing kernel

pistachio: add 5.15 testing kernel

Manually refreshed:
- 903-MIPS-DTS-img-marduk-Add-NXP-SC16IS752IPW.patch
- 905-MIPS-DTS-img-marduk-Add-led-aliases.patch (led node was renamed to led-1)

Automatically refreshed:
- 109-MIPS-DTS-img-marduk-switch-mmc-to-1-bit-mode.patch
- 401-mtd-nor-support-mtd-name-from-device-tree.patch
- 901-MIPS-DTS-img-marduk-Add-SPI-NAND-flash.patch
- 902-MIPS-DTS-img-marduk-Add-Cascoda-CA8210-6LoWPAN.patch
- 904-MIPS-DTS-img-marduk-Add-partition-name.patch

Enable testing kernel.

Co-Developed-by: Hauke Mehrtens <hauke@hauke-m.de>
Tested-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Nick Hainke <vincent@systemli.org>