ArmPlatformPkg/NorFlashDxe: use MmioWrite () not memory stores

ArmPlatformPkg/NorFlashDxe: use MmioWrite () not memory stores

When writing to the flash, make sure to use MmioWrite () wrappers instead
of letting the compiler generate the store instructions. This is needed
because under virtualization, store instructions with multiple outputs
(i.e., store pair or store with writeback) cannot be emulated efficiently
when operating on MMIO ranges.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-By: Olivier Martin <olivier.martin@arm.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16107 6f19259b-4bc3-4df7-8a09-765794883524