soc/intel/skylake/romstage: Increase size of postcar stack

I increase the size oof the postcar stack to prevent a stack overflow
during the measured boot feature. After common string functions have
been moved from inline into .c file
(https://review.coreboot.org/c/coreboot/+/32901), I experienced a stack
overflow in the postcar stage while verifiying the romstage during
measured boot. To prevent this, the stack size should be increased. To
play it safe, it should be increased to 8 KiB - though this is open for
discussion.

Change-Id: I6f1a4631bcadfb8c7d1de5bf0919e40990a65606
Signed-off-by: Christian Walter <christian.walter@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33434
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/soc/intel/skylake/romstage/romstage_fsp20.c

@@ -156,7 +156,7 @@ asmlinkage void car_stage_entry(void)
 	pmc_set_disb();
 	if (!s3wake)
 		save_dimm_info();
-	if (postcar_frame_init(&pcf, 1*KiB))
+	if (postcar_frame_init(&pcf, 8*KiB))
 		die("Unable to initialize postcar frame.\n");
 
 	/*