[QEMU] Fix QEMU boot issue in nested virtualization env

Is is reported that SBL QEMU target crashes when running in nested
virtualization env. For example, run QEMU with KVM flag inside
Ubuntu running on Windows Virtual Box.
After debug, it turned out somehow the KVM generated exception for
instruction "movd mm0, eax" at the very beginning. This was used to
save the CPU BIST info. If it is moved to be after switching to FLAT32
mode, then everything goes well.  This patch moved the BIST saving
into later stage in the boot in order to address the KVM crash issue.

This fixed #1469.

Signed-off-by: Maurice Ma <maurice.ma@intel.com>

BootloaderCorePkg/Stage1A/Ia32/Vtf0/Ia16/Init16.asm

@@ -35,7 +35,5 @@ EarlyInit16:
     ;
     ; ESP -  Initial value of the EAX register (BIST: Built-in Self Test)
     ;
-    movd     mm0, eax
-
     OneTimeCallRet EarlyInit16
 

BootloaderCorePkg/Stage1A/Ia32/Vtf0/Ia16/Real16ToFlat32.asm

@@ -105,6 +105,7 @@ TransitionFromReal16To32BitFlat:
     mov     ds, bx
     mov     bx, ADDR16_OF(gdtr)
 o32 lgdt    [cs:bx]
+    mov     ebx, eax ; save BIST to EBX
     mov     eax, cr0
     and     eax, SEC_DEFAULT_CR0_MASK
     or      eax, SEC_DEFAULT_CR0
@@ -120,5 +121,6 @@ jumpTo32BitAndLandHere:
     mov     fs, ax
     mov     gs, ax
     mov     ss, ax
+    movd    mm0, ebx  ; save BIST to MM0
     OneTimeCallRet TransitionFromReal16To32BitFlat