Platform HiKeyXXX: Use merged variable driver for emulated NV mode

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1323


Merge EmuVariable and Real variable driver.

The real variable driver has been updated to support emulated
variable NV mode and the EmuVariableRuntimeDxe will be removed
later, so use merged variable driver for emulated NV mode.

NOTE:
FaultTolerantWriteDxe is not needed at all for emulated NV mode,
so remove FaultTolerantWriteDxe including.

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