google/reef: Enable PS/2 keyboard driver by default

This device has a built-in keyboard that should be enabled by default
or it will not work in firmware.  This was tested to ensure that TAB
(display info) and Ctrl+D (enter developer mode) are functional at the
Chrome OS recovery screen.

BUG=chrome-os-partner:55549

Change-Id: I60156f1fc001b88deac69e03e02e9d8277fbc38d
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/15782
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/reef/Kconfig

@@ -33,6 +33,9 @@ config DRIVERS_I2C_DA7219
 config DRIVERS_I2C_GENERIC
 	default y
 
+config DRIVERS_PS2_KEYBOARD
+	default y
+
 config MAINBOARD_DIR
 	string
 	default google/reef