ArmVirtPkg: enable PE/COFF image and memory protection for ARM platforms

Like for AARCH64, enable PE/COFF image and NX memory protection for all
32-bit ARM virt platforms.

Note that this does not [yet] protect EfiLoaderData regions, due to
compatibility issues with GRUB.

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