arch/x86: Mark prepare_and_run_postcar noreturn

This moves the die() statement to a common place.

Change-Id: I24c9f00bfee169b4ca57b469c089188ec62ddada
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/65812
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/drivers/amd/agesa/romstage.c

@@ -76,7 +76,6 @@ void __noreturn romstage_main(void)
 
 	prepare_and_run_postcar();
 	/* We do not return. */
-	die("failed to load postcar\n");
 }
 
 static void ap_romstage_main(void)