REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1323 Merge EmuVariable and Real variable driver. Add PcdEmuVariableNvModeEnable (support both static and dynamic) to indicate if Variable driver will enable emulated variable NV mode. This patch prepares for adding emulated variable NV mode support in VariableRuntimeDxe. Cc: Jian J Wang <jian.j.wang@intel.com> Cc: Hao Wu <hao.a.wu@intel.com> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Star Zeng <star.zeng@intel.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Hao Wu <hao.a.wu@intel.com> Reviewed-by: Jian J Wang <jian.j.wang@intel.com> Tested-by: Julien Grall <julien.grall@arm.com> Acked-by: Julien Grall <julien.grall@arm.com>