RFC: layerscape: update to kernel 5.10

[Martin Schiller]

I have now found the cause of my boot problems with linux 5.10.
(see [1] for reference)

By changing the TEXT_OFFSET to 0x0 (instead of 0x80000 before) in the 
upstream
commit [2] and deactivated kernel option CONFIG_RELOCATABLE the system 
could not
boot.

Thus, we now need to set the KERNEL_LOADADDR to 0x80000000 in the 
layerscape
target for kernel >= 5.8. (ATTENTION: but then kernel 5.4 can no longer 
boot).

In addition, we should think about enabling CONFIG_RELOCATABLE in 
general to
avoid being completely in the dark in case of similar problems in the 
future.

Also, I am currently very unhappy with how the kernel patches are 
handled in the
layerscape target. So far they seem to be taken "1 to 1" from the NXP 
LSDK. This
pile of patches is totally unmanageable and it is impossible to 
understand what
is really needed and what is not.
There was already a small discussion about this [3].

I would like to make a clear CUT here and work as far as possible with 
the linux
upstream state.

What is your opinion about this?
(maybe any performance drawbacks, missing features etc.)

[1] 
http://lists.openwrt.org/pipermail/openwrt-devel/2021-October/036785.html
[2] https://www.spinics.net/lists/arm-kernel/msg798878.html
[3] 
http://lists.openwrt.org/pipermail/openwrt-devel/2021-February/033732.html