This reverts commit 3d2ae69f9c:
"ARM/SMP: Re-implement atomic exchange taking sel4 IPI into account"
Also removed riscv's try_arch_atomic_exchange_rlx().
This was added because CAS can take very long to finish on ARM if
the exclusive reservation granule (ERG) is large for the platform,
as any writes on other cores within up to 2Kb could make the CAS
fail.
The correct fix is to add padding around the global lock equal to ERG
to make CAS fast, which would make the extra IPI check redundant.
Signed-off-by: Indan Zupancic <Indan.Zupancic@mep-info.com>
17e968ad02