ArmPkg: introduce ASM_FUNC, MOV32/MOV64 and ADRL/LDRL macros

ArmPkg: introduce ASM_FUNC, MOV32/MOV64 and ADRL/LDRL macros

This introduces the ASM_FUNC() macro to annotate function entry points
in assembler files. This allows us to add additional metadata that
marks a function entry point as a function, and allows us to emit
a .section directive for each function, which makes it possible for
the linker to drop unreferenced code.

In addition, introduce a couple of utility macros that we can use to
clean up the code.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Eugene Cohen <eugene@hp.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>