IntelSiliconPkg IntelVTdPmrPei: Install IoMmu PPI before enabling PMR

IntelSiliconPkg IntelVTdPmrPei: Install IoMmu PPI before enabling PMR

Then the consumer of IoMmu PPI has opportunity to get granted DMA
buffer (by callback) to replace old buffer before it is forbidden
by enabling PMR.

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