ArmVirtPkg: Arm CCA configure system memory in early Pei

When a VMM creates a Realm, a small amount of DRAM (which contains
the firmware image) and the initial content is configured as Protected
RAM. The remaining System Memory is in the Protected Empty state. The
firmware must then initialise the remaining System Memory as Protected
RAM before it can be accessed.

Therefore, call the ArmCcaConfigureSystemMemory () in the early Pei
phase so that the System Memory is configured as Protected RAM.

Note: ArmCcaConfigureSystemMemory () is implemented in ArmCcaInitPeiLib
for which a Null implementation is provided. Therefore, this change
should not have an impact for non-Arm CCA enabled systems.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>