linux: userspace GPIO control

Allow use host GPIO pins for non-realtime purposes.

Signed-off-by: Andrey Kunitsyn <blackicebox@gmail.com>

src/linux/Makefile

@@ -4,7 +4,7 @@ dirs-y += src/linux src/generic
 
 src-y += linux/main.c linux/timer.c linux/console.c linux/watchdog.c
 src-y += linux/pca9685.c linux/spidev.c linux/analog.c linux/hard_pwm.c
-src-y += linux/i2c.c generic/crc16_ccitt.c generic/alloc.c
+src-y += linux/i2c.c linux/gpio.c generic/crc16_ccitt.c generic/alloc.c
 
 CFLAGS_klipper.elf += -lutil