ArmPkg/AsmMacroIoLib: remove unused obsolete MMIO and other asm macros

ArmPkg/AsmMacroIoLib: remove unused obsolete MMIO and other asm macros

This removes the various Mmio ASM macros that are not used anywhere in
the code, and removes some variants of LoadConstant... () that are not
used anywhere either.

Note that these MmioXxx() implementations are unrelated to the C versions
defined in MdePkg. These are strictly intended for use in assembler, and
no such uses remain.

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