ArmPlatformPkg/ArmVExpressLibCTA15-A7: Mapped the extra 1GB of DRAM in the MMU

ArmPlatformPkg/ArmVExpressLibCTA15-A7: Mapped the extra 1GB of DRAM in the MMU

ARM Versatile Express TC2 Core Tile has two profiles: the 1GB DRAM core tile or
the 2GB DRAM core tile profiles.
By default UEFI assumes, it is the 1GB core tile. In case of 2GB DRAM it declares
this additional 1GB resource system memory to UEFI. But the previous code did
not map this memory in the MMU Page Table.
So, the memory was allocatable by UEFI modules, but was not accessible by the CPU
(because not mapped).

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Leif Lindholm <Leif.Lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14449 6f19259b-4bc3-4df7-8a09-765794883524