DynamicTablesPkg: Rename enum used for ID Mapping

DynamicTablesPkg: Rename enum used for ID Mapping

This patch was originally merged in edk2 master at
1d49a75367ef6827b8b8f77f61e9ce245d1bdee3. However, this was
later reverted at 334111b0dab80394aeb1ebb8f0f3314847e2dc1f
as it was merged during the Soft Feature Freeze for
edk2-stable201903.

Resubmitting this patch as the edk2 merge window is now open.

Renamed the enum EArmObjIdMapping to EArmObjIdMappingArray
and updated the IORT generator accordingly.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Alexei Fedorov <alexei.fedorov@arm.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <alexei.fedorov@arm.com>