Input: gpio-keys - add support for linux,input-value DTS property

Allows setting the value of EV_ABS events from DTS.
This property is included in the gpio-keys.yaml scheme, but was only
implemented for gpio-keys-polled.

Signed-off-by: Gergo Koteles <soyer@irl.hu>
Link: https://lore.kernel.org/r/3519a11b0ef5324a2befbd137cd2aa0cb8fd057d.1676850819.git.soyer@irl.hu


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>