BaseUefiCpuLib: Preserve EBX register in InitializeFloatingPointUnits

The EBX register should be preserved for the IA32 C calling convention.
The use of the CPUID instruction was modifying the EBX register, so
we push and pop EBX.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9573 6f19259b-4bc3-4df7-8a09-765794883524

UefiCpuPkg/Library/BaseUefiCpuLib/Ia32/InitializeFpu.asm

@@ -30,15 +30,18 @@ mMmxControlWord       DD      01F80h
     .xmm
     .code
 
-;
+;
 ; Initializes floating point units for requirement of UEFI specification.
 ;
 ; This function initializes floating-point control word to 0x027F (all exceptions
 ; masked,double-precision, round-to-nearest) and multimedia-extensions control word
 ; (if supported) to 0x1F80 (all exceptions masked, round-to-nearest, flush to zero
-; for masked underflow).
+; for masked underflow).
 ;
 InitializeFloatingPointUnits PROC PUBLIC
+
+    push    ebx
+
     ;
     ; Initialize floating point units
     ;
@@ -67,6 +70,7 @@ InitializeFloatingPointUnits PROC PUBLIC
     ;
     ldmxcsr mMmxControlWord
 Done:
+    pop     ebx
 
     ret