MdePkg: Add ACPI Low Power Idle Table (LPIT) definitions

MdePkg: Add ACPI Low Power Idle Table (LPIT) definitions

ACPI Low Power Idle Table (LPIT) Revision 001, dated July 2014
http://www.uefi.org/sites/default/files/resources/ACPI_Low_Power_Idle_Table.pdf

Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>