ArmVirtPkg: add name GUIDs to FvMain instances

ArmVirtPkg: add name GUIDs to FvMain instances

Assign name GUIDs to the FVs that may appear in DevicePath references to
things like the UiApp and the UEFI Shell. This prevents these device
paths from changing inadvertently when the FV ends up in a different
memory location due to external occurrences such as, e.g., a change in
the amount of system memory.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>