ArmPkg/ProcessorSubClassDxe: Get processor version from OemMiscLib

ArmPkg/ProcessorSubClassDxe: Get processor version from OemMiscLib

In some scenarios, the processor version may be updated dynamically
from pre-UEFI firmware during booting. But the processor version is
fixed with PCD (PcdProcessorVersion), so it can not be updated it
dynamically. This patch will support setting that value both
statically and dynamically.

Signed-off-by: Nhi Pham <nhi@os.amperecomputing.com>
Reviewed-by: Rebecca Cran <rebecca@quicinc.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Leif Lindholm <quic_llindhol@quicinc.com>