apm821xx: add support for kernel 5.15 for testing

apm821xx: add support for kernel 5.15 for testing

This patch copies over refreshed config and patches from 5.10
with the following changes:

 - dropped superfluous tc654/tc655 variant detection patch
   (tc654 support will become available upstream starting with
   5.17-rc7+).

 - dropped xhci msi(x) workaround... as the broken MSI(X)
   is now gone.

 - dropped dwc2 workaround since the driver was fixed and it
   works without it.

Please note: Netgear WNDAP660 & WNDAP620 users:

Due to the kernel's size increase, uboot will likely break
because it is overwrite the kernel during decompression.

To fix this (and debrick affected devices, no reflash
necessary), attach the RJ45-Serial-Console cable and
enter the following in the uboot prompt during bootup:

 setenv kernel_addr_r 1100000
 saveenv
 run bootcmd

to restore the old/previous behavior:

 setenv kernel_addr_r 600000
 saveenv
 run bootcmd

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>