gpiolib: devres: Get rid of unused devm_gpio_free()

The last user, which in fact was a dead code, has gone a year ago,
previous one 3 years ago. On top of that we want to drop away the
legacy GPIO APIs in the kernel, so take a chance to get rid of
unused devm_gpio_free() and accompanying stuff.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>