arch/x86/postcar_loader.c: Change prepare_and_run_postcar signature

The postcar frame can now be a local variable to that function.

Change-Id: I873298970fff76b9ee1cae7da156613eb557ffbc
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61964
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/cpu/intel/car/romstage.c

@@ -14,8 +14,6 @@
    following as a guideline for acceptable stack usage. */
 #define DCACHE_RAM_ROMSTAGE_STACK_SIZE 0x2000
 
-static struct postcar_frame early_mtrrs;
-
 static void romstage_main(void)
 {
 	int i;
@@ -54,7 +52,7 @@ static void romstage_main(void)
 	if (CONFIG(SMM_TSEG))
 		smm_list_regions();
 
-	prepare_and_run_postcar(&early_mtrrs);
+	prepare_and_run_postcar();
 	/* We do not return here. */
 }