intel/amenia: Add MAINBOARD_FAMILY for amenia

BUG=chrome-os-partner:51844
TEST=Boot to chrome

Change-Id: I66178cc75872f14941434081d9650a569a084d04
Signed-off-by: Bora Guvendik <bora.guvendik@intel.com>
Reviewed-on: https://review.coreboot.org/16135
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/intel/amenia/Kconfig

@@ -25,6 +25,10 @@ config MAINBOARD_DIR
 	string
 	default intel/amenia
 
+config MAINBOARD_FAMILY
+	string
+	default "Intel_Amenia"
+
 config MAINBOARD_PART_NUMBER
 	string
 	default "Amenia"