ArmPlatformPkg: remove EFI_MEMORY_UC attribute from normal memory

ArmPlatformPkg: remove EFI_MEMORY_UC attribute from normal memory

On ARM systems, mapping normal memory as device memory may have unintended
side effects, given that unaligned accesses or loads and stores with special
semantics (e.g., load/store exclusive) may fault or may not work as expected.
Similarly, DC ZVA instructions are only supported on normal memory, not
device memory.

So remove the EFI_MEMORY_UC attribute that we set by default on system RAM.
If any region requires this attribute, it is up to the driver to set this
attribute, and to ensure that no offending operations are performed on it.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>