mainboard/google/kahlee: Add MAINBOARD_FAMILY

BUG=b:68865273

Change-Id: Ia2e9b10035e9dd502a563cdf8324ea8ea1922db3
Signed-off-by: Lann Martin <lannm@chromium.org>
Reviewed-on: https://review.coreboot.org/22359
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/mainboard/google/kahlee/Kconfig

@@ -47,6 +47,10 @@ config DEVICETREE
 	string
 	default "variants/${CONFIG_VARIANT_DIR}/devicetree.cb"
 
+config MAINBOARD_FAMILY
+	string
+	default "Google_Kahlee"
+
 config MAX_CPUS
 	int
 	default 4