UefiCpuPkg: Solve that stack top address is not mapped in pagetable

For the case CPU logic index is 0, RSP points to the very top of all AP
stacks. That address is not mapped in page table.

Cc: Guo Dong <guo.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Sean Rhodes <sean@starlabs.systems>
Cc: James Lu <james.lu@intel.com>
Cc: Gua Guo <gua.guo@intel.com>
Signed-off-by: Ted Kuo <ted.kuo@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>

UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm

@@ -315,6 +315,7 @@ MwaitCheckGeneric:
 MwaitLoopGeneric:
     cli
     mov        rax, rsp           ; Set Monitor Address
+    sub        eax, 8             ; To ensure the monitor address is in the page table
     xor        ecx, ecx           ; ecx = 0
     xor        edx, edx           ; edx = 0
     monitor