intel: Fix romstage main() with asmlinkage

Backport from haswell.

Change-Id: I585639f8af47bd1d8c606789ca026c6d2d0cc785
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15225
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/cpu/intel/car/romstage.c

@@ -0,0 +1,7 @@
+#include <cpu/intel/romstage.h>
+
+void * asmlinkage romstage_main(unsigned long bist)
+{
+	mainboard_romstage_entry(bist);
+	return (void*)CONFIG_RAMTOP;
+}

src/include/cpu/intel/romstage.h

@@ -1,7 +1,12 @@
 #ifndef _CPU_INTEL_ROMSTAGE_H
 #define _CPU_INTEL_ROMSTAGE_H
 
+#include <arch/cpu.h>
+
 /* std signature of entry-point to romstage.c */
 void main(unsigned long bist);
 
+void mainboard_romstage_entry(unsigned long bist);
+void * asmlinkage romstage_main(unsigned long bist);
+
 #endif /* _CPU_INTEL_ROMSTAGE_H */