gpiolib: split character device into gpiolib-cdev

Split the cdev specific functionality out of gpiolib.c and into
gpiolib-cdev.c. This improves the readability and maintainability of both
the cdev and core gpiolib code.

Suggested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20200616093615.5167-1-warthog618@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Makefile

@@ -7,6 +7,7 @@ obj-$(CONFIG_GPIOLIB)		+= gpiolib.o
 obj-$(CONFIG_GPIOLIB)		+= gpiolib-devres.o
 obj-$(CONFIG_GPIOLIB)		+= gpiolib-legacy.o
 obj-$(CONFIG_GPIOLIB)		+= gpiolib-devprop.o
+obj-$(CONFIG_GPIOLIB)		+= gpiolib-cdev.o
 obj-$(CONFIG_OF_GPIO)		+= gpiolib-of.o
 obj-$(CONFIG_GPIO_SYSFS)	+= gpiolib-sysfs.o
 obj-$(CONFIG_GPIO_ACPI)		+= gpiolib-acpi.o

drivers/gpio/gpiolib-cdev.h

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef GPIOLIB_CDEV_H
+#define GPIOLIB_CDEV_H
+
+#include <linux/device.h>
+
+int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt);
+void gpiolib_cdev_unregister(struct gpio_device *gdev);
+
+#endif /* GPIOLIB_CDEV_H */