greybus: makefile: add requirement for CONFIG_INPUT

To support key events coming from the svc (ara key) it is needed to add
the input core as an required config option.
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Makefile

@@ -51,7 +51,7 @@ INSTALL_MOD_PATH	?= /..
 PWD			:= $(shell pwd)
 
 # kernel config option that shall be enable
-CONFIG_OPTIONS_ENABLE := POWER_SUPPLY PWM SYSFS SPI USB SND_SOC MMC LEDS_CLASS
+CONFIG_OPTIONS_ENABLE := POWER_SUPPLY PWM SYSFS SPI USB SND_SOC MMC LEDS_CLASS INPUT
 
 # kernel config option that shall be disable
 CONFIG_OPTIONS_DISABLE :=