google/sand: Add keyboard backlight support

BUG=None
TEST=emerge-sand coreboot chromeos-bootimage and verify the keyboard
backlight can be bright and  alt+f6, alt+f7 function keys can be used.

Change-Id: I86a35551a9348ff6ad26dfccd3b2786282d56069
Signed-off-by: Katherine Hsieh <Katherine.Hsieh@quantatw.com>
Reviewed-on: https://review.coreboot.org/19479
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/mainboard/google/reef/variants/sand/include/variant/ec.h b/src/mainboard/google/reef/variants/sand/include/variant/ec.h
index 80cf806..e4377c8 100644
--- a/src/mainboard/google/reef/variants/sand/include/variant/ec.h
+++ b/src/mainboard/google/reef/variants/sand/include/variant/ec.h
@@ -62,6 +62,9 @@
 /* Enable EC backed ALS device in ACPI */
 #define EC_ENABLE_ALS_DEVICE
 
+/* Enable EC backed Keyboard Backlight in ACPI */
+#define EC_ENABLE_KEYBOARD_BACKLIGHT
+
 /* Enable EC backed PD MCU device in ACPI */
 #define EC_ENABLE_PD_MCU_DEVICE