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/soc/intel/apollolake/romstage.c

@@ -240,7 +240,7 @@ asmlinkage void car_stage_entry(void)
 	else
 		printk(BIOS_ERR, "Failed to determine variable data\n");
 
-	if (postcar_frame_init(&pcf, 1*KiB))
+	if (postcar_frame_init(&pcf, 0))
 		die("Unable to initialize postcar frame.\n");
 
 	mainboard_save_dimm_info();