MdePkg: restrict UefiMultiPhase.h contents if VFRCOMPILE defined

MdePkg: restrict UefiMultiPhase.h contents if VFRCOMPILE defined

Turns out all .vfr files in the tree interacting with DynamicPcds
manually copy the same set of EFI_VARIABLE_* definitions, since the rest
of UefiMultiPhase.h is incompatible with VfrCompile.

For now, reshuffle these definitions to the start of the file, and put
the rest of the file behind #ifndef VFRCOMPILE to permit direct
inclusion in .vfr source files.

https://bugzilla.tianocore.org/show_bug.cgi?id=878 has been raised to
request VfrCompile is extended to support the original format.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>