[Linaro-uefi] ArmVirtualizationPkg name change

Hi all,

As part of the promotion of the ArmVirtualizationPkg/ to a top-level Tianocore package, we used the opportunity to shorten its name (and other derived names).

So the new top level package will be called ArmVirtPkg/. Other occurrences have been shortened as well, e.g., the QEMU platform DSC is now called ArmVirtPkg/ArmVirtQemu.dsc, and the AArch64 targeted build will be created in Build/ArmVirtQemu-AARCH64/

This change is effective immediately: the change has been submitted to the authoritative Subversion server, so the change will be synced to GitHub later today.

Regards, Ard.