arch/x86: Add a common romstage entry

It might be possible to have this used for more than x86, but that
will be for a later commit.

Change-Id: I4968364a95b5c69c21d3915d302d23e6f1ca182f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55067
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>

src/soc/amd/picasso/romstage.c

@@ -8,19 +8,13 @@
 #include <console/console.h>
 #include <fsp/api.h>
 #include <program_loading.h>
-#include <timestamp.h>
+#include <romstage_common.h>
 #include <types.h>
 
-asmlinkage void car_stage_entry(void)
+void __noreturn romstage_main(void)
 {
-	timestamp_add_now(TS_ROMSTAGE_START);
-
 	post_code(0x40);
 
-	console_init();
-
-	post_code(0x42);
-
 	/* Snapshot chipset state prior to any FSP call. */
 	fill_chipset_state();
 
@@ -33,4 +27,5 @@ asmlinkage void car_stage_entry(void)
 	run_ramstage();
 
 	post_code(0x50); /* Should never see this post code. */
+	die("failed to load ramstage\n");
 }