gm45: Recognize 48MiB gfx UMA.

Change-Id: I33e6b357ea044d6ec00b119e84cbada7bf58317f
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/6685
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

src/northbridge/intel/gm45/ram_calc.c

@@ -43,6 +43,8 @@ u32 decode_igd_memory_size(const u32 gms)
 		return  16 << 10;
 	case 5:
 		return  32 << 10;
+	case 6:
+		return  48 << 10;
 	case 7:
 		return  64 << 10;
 	case 8: