ArmPkg/ArmLib: add accessor function for Cache Writeback Granule

ArmPkg/ArmLib: add accessor function for Cache Writeback Granule

Add a function to ArmLib that provides access to the Cache Writeback
Granule (CWG) field in CTR_EL0. This information is required when
performing non-coherent DMA.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18758 6f19259b-4bc3-4df7-8a09-765794883524