MdeModulePkg DxeCore: Check FvImage alignment

MdeModulePkg DxeCore: Check FvImage alignment

No need to allocate aligned buffer if FvImage has been
at required alignment.

Then the code logic will be aligned with ProcessFvFile() in
MdeModulePkg/Core/Pei/FwVol/FwVol.c.

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>