ArmPkg/ArmLib ARM: set .fpu to let Clang 7 assemble ArmV7Support.S

ArmPkg/ArmLib ARM: set .fpu to let Clang 7 assemble ArmV7Support.S

Clang 7 complains about the vmsr instruction in ArmV7Support.S,
which is only available on cores that implement some flavour of
VFP. So set the .fpu to NEON like we do in some other places.

Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>