MdeModulePkg: use central variable definitions in DriverSampleDxe
MdeModulePkg: use central variable definitions in DriverSampleDxe

Use UefiMultiPhase.h in Vfr.vfr instead of duplicating EFI_VARIABLE_*
definitions.

Cc: Star Zeng <5c6bb72efe464613af94e84c05522a361b23844a@intel.com>
Cc: Eric Dong <fa9eeec52367040ac98013bc4b2913db170588f8@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Leif Lindholm <a613079f0455438b29e28a9c5b9eb3779a81a33a@linaro.org>
Reviewed-by: Star Zeng <5c6bb72efe464613af94e84c05522a361b23844a@intel.com>

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