arch/x86/*.S: use defines instead of hardcoded values

As preparation for x86_64 clean the assembly code and introduce
arch/ram_segs.h similar to existing arch/rom_segs.h.

Replace open coded segment values with the defines from the new
header.

Change-Id: Ib006cd4df59951335506b8153e9347450ec3403e
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36321
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/x86/sipi_vector.S

@@ -15,15 +15,12 @@
 #include <cpu/x86/cr.h>
 #include <cpu/amd/mtrr.h>
 #include <cpu/x86/msr.h>
+#include <arch/ram_segs.h>
 
 /* The SIPI vector is responsible for initializing the APs in the system. It
  * loads microcode, sets up MSRs, and enables caching before calling into
  * C code. */
 
-/* These segment selectors need to match the gdt entries in c_start.S. */
-#define CODE_SEG 0x10
-#define DATA_SEG 0x18
-
 .section ".module_parameters", "aw", @progbits
 ap_start_params:
 gdtaddr:
@@ -83,10 +80,10 @@ _start:
 	orl	$CR0_SET_FLAGS, %eax
 	movl	%eax, %cr0
 
-	ljmpl	$CODE_SEG, $1f
+	ljmpl	$RAM_CODE_SEG, $1f
 1:
 	.code32
-	movw	$DATA_SEG, %ax
+	movw	$RAM_DATA_SEG, %ax
 	movw	%ax, %ds
 	movw	%ax, %es
 	movw	%ax, %ss