ArmPkg: add ArmHasSecurityExtensions () helper function

ArmPkg: add ArmHasSecurityExtensions () helper function

Create a helper function to eliminate direct feature register reading.

Returns BOOLEAN True if the CPU implements the Security extensions,
otherwise returns BOOL False.

This function is only implemented for ARM, not AArch64.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Leif Lindholm <leif@nuviainc.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>