ArmVirtPkg: Add Kvmtool RTC Fdt Client Library

ArmVirtPkg: Add Kvmtool RTC Fdt Client Library

Add library that parses the Kvmtool device tree and updates
the dynamic PCDs describing the RTC Memory map.

It also maps the MMIO region used by the RTC as runtime memory
so that the RTC registers are accessible post ExitBootServices.

Since UEFI takes ownership of the RTC hardware disable the RTC
node in the DT to prevent the OS from attaching its device
driver as well.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>