greybus: build: add pwm to config options to enable

Add PWM to the kernel config options that shall be enabled.

When PWM is not enabled connection init will fail with

	greybus endo0:3:4:9:9: failed to register PWM: -22

when using the default manifest.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
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 := SYSFS SPI USB SND_SOC MMC LEDS_CLASS
+CONFIG_OPTIONS_ENABLE := PWM SYSFS SPI USB SND_SOC MMC LEDS_CLASS
 
 # kernel config option that shall be disable
 CONFIG_OPTIONS_DISABLE :=