ArmPkg/ArmMmuLib: Add MMU Library suitable for use in S-EL0.

ArmPkg/ArmMmuLib: Add MMU Library suitable for use in S-EL0.

The Standalone MM environment runs in S-EL0 in AArch64 on ARM Standard
Platforms. Privileged firmware e.g. ARM Trusted Firmware sets up its
architectural context including the initial translation tables for the
S-EL1/EL0 translation regime. The MM environment will still request ARM
TF to change the memory attributes of memory regions during
initialization.

The Standalone MM image is a FV that encapsulates the MM foundation
and drivers. These are PE-COFF images with data and text segments.
To initialise the MM environment, Arm Trusted Firmware has to create
translation tables with sane default attributes for the memory
occupied by the FV. This library sends SVCs to ARM Trusted Firmware
to request memory permissions change for data and text segments.

This patch adds a simple MMU library suitable for execution in S-EL0 and
requesting memory permissions change operations from Arm Trusted Firmware.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>