google/auron: Clean up variant-specific romstage code

Use an empty weak function for variant_romstage_entry(), rather than
having separate empty functions for boards which don't utilize it.

Change-Id: I7a278ed716484bea377a5dd98d4a534502c8bab6
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/28612
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/google/auron/romstage.c

@@ -25,6 +25,10 @@
 #include <variant/spd.h>
 #include "variant.h"
 
+__weak void variant_romstage_entry(struct romstage_params *rp)
+{
+}
+
 void mainboard_romstage_entry(struct romstage_params *rp)
 {
 	struct pei_data pei_data;
@@ -43,6 +47,6 @@ void mainboard_romstage_entry(struct romstage_params *rp)
 	/* Call into the real romstage main with this board's attributes. */
 	romstage_common(rp);
 
-	/* Do variant-specific (read: Samus) init */
+	/* Do variant-specific init */
 	variant_romstage_entry(rp);
 }

src/mainboard/google/auron/variants/auron_paine/variant.c

@@ -12,7 +12,6 @@
  */
 
 #include <smbios.h>
-#include <soc/romstage.h>
 #include <variant/onboard.h>
 #include <mainboard/google/auron/variant.h>
 
@@ -32,8 +31,3 @@ int variant_smbios_data(device_t dev, int *handle,
 
 	return len;
 }
-
-void variant_romstage_entry(struct romstage_params *rp)
-{
-	/* N/A for boards other than SAMUS */
-}

src/mainboard/google/auron/variants/auron_yuna/variant.c

@@ -12,7 +12,6 @@
  */
 
 #include <smbios.h>
-#include <soc/romstage.h>
 #include <variant/onboard.h>
 #include <mainboard/google/auron/variant.h>
 
@@ -32,8 +31,3 @@ int variant_smbios_data(device_t dev, int *handle,
 
 	return len;
 }
-
-void variant_romstage_entry(struct romstage_params *rp)
-{
-	/* N/A for boards other than SAMUS */
-}