ArmVirtPkg: introduce ArmVirtMemInfoLib library class

ArmVirtPkg: introduce ArmVirtMemInfoLib library class

As part of the effort to get rid of ArmPlatformLib (which incorporates
far too many duties in a single library), introduce ArmVirtMemInfoLib
which will be invoked by our ArmVirtMemoryInitPeiLib implementation to
get a description of the virtual address space. This will allow us to
remove this functionality from ArmPlatformLib later, or, in the case of
ArmVirtXen and ArmVirtQemuKernel, drop ArmPlatformLib altogether.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>