Merge branch '2022-03-02-armv8-fixes-and-cleanups' into next

To quote the author:
I was looking into the arm64 boot code lately and stumbled upon some
issues. Also Nishanth brought back memories of a lengthy debug session,
which was caused due to U-Boot keeping SErrors masked. As the resulting
patches are all somewhat related, I gathered this series here to address
those problems.

Patches 1 to 3 address exception handling issues, with the SError
enablement being the most prominent fix here.
Patch 4 cleans up asm/io.h. This was on the list before[1], but was
somehow lost when it was intercepted by a shorter version of itself.
Patches 5 and 6 clean up some unnecessarily complicated AArch64 assembly
code.