core: relax gpiod_is_gpiochip_device() even more

core: relax gpiod_is_gpiochip_device() even more

Currently libgpiod requires that the GPIO chip character device be named
'gpiochip%u' in devfs. However it's a perfectly valid use-case to have
the device file renamed by udev (or equivalent) to anything else.

Modify gpiod_is_gpiochip_device() to check the major and minor device
numbers first and then ensure that the device in question is associated
with the GPIO subsystem. No longer check the name.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>