MdePkg/SmmIoLib: Add header file.

This SmmIoLib is used to check if an IO resource
is valid in SMM.

Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>