platform/x86: x86-android-tablets: Add x86_android_tablet_get_gpiod() helper

Factor the code to go from a gpiochip label + pin-numer to a gpio_desc
out of x86_acpi_irq_helper_get() and make it into a new
x86_android_tablet_get_gpiod() helper, as this will be necessary in some
x86_dev_info.init() functions too.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220205191356.225505-3-hdegoede@redhat.com