MdePkg/BaseLib: Add stack switch related definitions for IA32

MdePkg/BaseLib: Add stack switch related definitions for IA32

The new definitions include two structures

  IA32_TASK_STATE_SEGMENT
  IA32_TSS_DESCRIPTOR

two macros

  IA32_GDT_TYPE_TSS
  IA32_GDT_ALIGNMENT

and one API

  VOID
  EFIAPI
  AsmWriteTr (
    IN UINT16 Selector
    );

They're needed to setup task gate and interrupt stack table for stack switch.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Suggested-by: Ayellet Wolman <ayellet.wolman@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Jeff Fan <vanjeff_919@hotmail.com>
Reviewed-by: Jiewen.yao@intel.com