mainboard/google/reef: unconditionally set MAINBOARD_FAMILY

For all mainboard variants use the "Google_Reef" family by default
which is populated in SMBIOS tables. A variant can provide their own
value if needed, but "Google_Reef" can reside as the family without
having to add conditions for each variant when MAINBOARD_FAMILY
have to be overridden.

BUG=chrome-os-partner:56677

Change-Id: Ic214eae1e6473b32f4cb442c09c34355357e1257
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/16813
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins)

src/mainboard/google/reef/Kconfig

@@ -61,7 +61,7 @@ config MAINBOARD_PART_NUMBER
 
 config MAINBOARD_FAMILY
 	string
-	default "Google_Reef" if BOARD_GOOGLE_REEF
+	default "Google_Reef"
 
 config GBB_HWID
 	string