MdePkg NASM Thunk16: Work around NASM 2.09.04 - 2.10rc1 bug

Without this change, NASM 2.09.04 will hang with OVMF+CSM on both IA32
and X64.

Tested on OVMF+CSM on GCC49 with NASM 2.07, 2.09.04 and 2.11.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16058 6f19259b-4bc3-4df7-8a09-765794883524
MdePkg NASM Thunk16: Add missing ASM_PFX for InternalAsmThunk16

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16059 6f19259b-4bc3-4df7-8a09-765794883524