cpu/x86/cpu_info.S: Remove ebx save/restore

The push/pop of %ebx was only added because smm_stub saves the canary
value in it. Now that we no longer use cpu_info in smm, we no longer
need to save the register.

BUG=b:179699789
TEST=Boot guybrush to the OS

Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Change-Id: I554dbe016db8b1c61246c8ffc7fa252b2542ba92
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58205
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/cpu/x86/cpu_info.S.inc

@@ -28,12 +28,11 @@
  * @desc_index: Index of the descriptor in the table. Defaults to 0. Must be a
  *              register if specified.
  *
- * Clobbers %eax.
+ * Clobbers %eax, %ebx.
  */
 .macro set_segment_descriptor_base desc_array:req, base:req, desc_index
 	mov	\base, %eax
 
-	push	%ebx /* preserve ebx */
 	mov	\desc_array, %ebx
 
 .ifb \desc_index
@@ -50,5 +49,4 @@
 	movb	%al, 7(%ebx, \desc_index, 8)
 .endif
 
-	pop	%ebx
 .endm