soc/amd/genoa: Implement romstage

The only thing romstage needs to do is find cbmem_top.

TESTED: reaches ramstage.

Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Change-Id: Ic2837c4a2b0ec8dcd9dd99602f9c073999c36139
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76514
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Varshit Pandya <pandyavarshit@gmail.com>

src/soc/amd/genoa/romstage.c

@@ -1,10 +1,16 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <amdblocks/post_codes.h>
+#include <amdblocks/memmap.h>
+#include <cbmem.h>
+#include <program_loading.h>
 #include <romstage_common.h>
-#include <halt.h>
 
 void __noreturn romstage_main(void)
 {
-	/* Needed for __noreturn */
-	halt();
+	post_code(POSTCODE_ROMSTAGE_MAIN);
+
+	cbmem_initialize_empty();
+	memmap_stash_early_dram_usage();
+	run_ramstage();
 }