ArmVirtPkg/ArmVirtMemoryInitPeiLib: avoid redundant cache invalidation

ArmVirtPkg/ArmVirtMemoryInitPeiLib: avoid redundant cache invalidation

Alex reports that the cache invalidation performed by
ArmVirtMemoryInitPeiLib takes a non-negligible amount of time at boot.
This cache invalidation used to be necessary to avoid inconsistencies
between the CPU's cached and uncached views of the permanent PEI memory
region, given that the PEI phase is where the MMU gets enabled.

The only allocations done from permanent PEI memory with the MMU off are
pages used for page tables, and since commit 748fea6279ef
("ArmPkg/ArmMmuLib AARCH64: invalidate page tables before populating
them"), each of those is invalidated in the caches explicitly, for
reasons described in the patch's commit log. All other allocations done
in PEI are either from temporary PEI memory, which includes the stack,
or from permanent PEI memory but after the MMU has been enabled.

This means that the cache invalidation in ArmVirtMemoryInitPeiLib is no
longer necessary, and can simply be dropped.

Reported-by: Alexander Graf <graf@amazon.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>