arch/x86: Adjust size of postcar stack

With VBOOT=y && VBOOT_MEASURED_BOOT=y message
digest will be allocated from the stack and
1 KiB reserve used with the recent platforms
was no longer sufficient.

The comment of LZMA scratchpad consuming stack
was obsolete for postcar, so these can be reduced
to same 4 KiB.

Change-Id: Iba1fb5bfad6946f316feac2d8c998a782142a56a
Signed-off-by: Mario Scheithauer <mario.scheithauer@siemens.com>
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33775
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/cpu/intel/haswell/romstage.c

@@ -38,8 +38,6 @@
 #include <cpu/intel/romstage.h>
 #include "haswell.h"
 
-#define ROMSTAGE_RAM_STACK_SIZE 0x5000
-
 /* platform_enter_postcar() determines the stack to use after
  * cache-as-ram is torn down as well as the MTRR settings to use,
  * and continues execution in postcar stage. */
@@ -48,7 +46,7 @@ void platform_enter_postcar(void)
 	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, ROMSTAGE_RAM_STACK_SIZE))
+	if (postcar_frame_init(&pcf, 0))
 		die("Unable to initialize postcar frame.\n");
 	/* Cache the ROM as WP just below 4GiB. */
 	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);