boot: zephyr: Fix indication LED not selecting GPIO

Makes indication LED Kconfig select GPIO so that it can work.

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index 8a73728..41daac8 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -498,7 +498,7 @@
 
 config MCUBOOT_INDICATION_LED
 	bool "Turns on LED indication when device is in DFU"
-	default n
+	select GPIO
 	help
 	  Device device activates the LED while in bootloader mode.
 	  mcuboot-led0 alias must be set in the device's .dts