mb/google/poppy/variants/nami: Provide implementation of mainboard_vbt_filename

This change adds board-specific implementation of
mainboard_vbt_filename which returns "vbt.bin" by default. This is in
preparation to allow multiple vbt binaries to be added to single
image. More sku_id specific names will be added in follow-up CLs.

BUG=b:79396300

Change-Id: I3821d55bfbe9e5773bd2eb0b0003045a80158d8c
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/26227
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/mainboard/google/poppy/variants/nami/mainboard.c

@@ -21,6 +21,7 @@
 #include <commonlib/cbfs_serialized.h>
 #include <compiler.h>
 #include <device/device.h>
+#include <drivers/intel/gma/opregion.h>
 #include <ec/google/chromeec/ec.h>
 #include <smbios.h>
 #include <soc/ramstage.h>
@@ -139,3 +140,14 @@ const char *smbios_mainboard_manufacturer(void)
 
 	return manuf;
 }
+
+const char *mainboard_vbt_filename(void)
+{
+	uint32_t sku_id = variant_board_sku();
+
+	switch (sku_id) {
+	default:
+		return "vbt.bin";
+		break;
+	}
+}