Add RS780 defaut graphics ID to AMD Mahogany mainboard.

Added the default ID to the mainboard Kconfig.

Change-Id: Ie5d39ccdda9d4f5a86214b5bd9ca629070ff152a
Signed-off-by: Marc Jones <marcj303@gmail.com>
Reviewed-on: http://review.coreboot.org/488
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)

src/mainboard/amd/mahogany/Kconfig

@@ -73,4 +73,8 @@ config IRQ_SLOT_COUNT
 	int
 	default 11
 
+config VGA_BIOS_ID
+	string
+	default "1002,9615"
+
 endif # BOARD_AMD_MAHOGANY

src/mainboard/amd/mahogany_fam10/Kconfig

@@ -83,4 +83,8 @@ config RAMBASE
 	hex
 	default 0x200000
 
+config VGA_BIOS_ID
+	string
+	default "1002,9615"
+
 endif # BOARD_AMD_MAHOGANY_FAM10