efi_loader: Rename and correct values for ARM_SMC_MM_*

Instead of adding the definition for the specific MM SVC used in
StandAloneMM we added the one used in the standard SMC calls.
So change the value from -4 to -5 to match the correct one defined in
EDK2 and rename them to avoid future confusion

Fixes 23a397d2: ("efi_loader: Add headers for EDK2 StandAloneMM communication")
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>