MdeModulePkg/EmmcBlockIoPei: Support IoMmu

MdeModulePkg/EmmcBlockIoPei: Support IoMmu

Update the EmmcBlockIoPei driver to consume IOMMU_PPI to allocate DMA
buffer.

If no IOMMU_PPI exists, this driver still calls PEI service
to allocate DMA buffer, with assumption that DRAM==DMA.

This is a compatible change.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>