gpiolib: fix sysfs when cdev is not selected

In gpiochip_setup_dev() the call to gpiolib_cdev_register() indirectly
calls device_add(). This is still required for the sysfs even when
CONFIG_GPIO_CDEV is not selected in the build.

Replace the stubbed functions in gpiolib-cdev.h with macros in gpiolib.c
that perform the required device_add() and device_del() when
CONFIG_GPIO_CDEV is not selected.

Fixes: d143493c01b7 (gpiolib: make cdev a build option)
Reported-by: Nicolas Schichan <nschichan@freebox.fr>
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Tested-by: Nicolas Schichan <nschichan@freebox.fr>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

gpiolib: Update header block in gpiolib-cdev.h

The dev_t is defined in types.h while struct gpio_device forward declaration
is missed. Take into account above and update header block in gpiolib-cdev.h.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20201005095622.73616-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

gpiolib: make cdev a build option

Make the gpiolib-cdev module a build option. This allows the CDEV
interface to be removed from the kernel to reduce kernel size in
applications where is it not required, and provides the parent for
other CDEV interface specific build options to follow.

Suggested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

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>