gpio_monitor: Allow multiple callbacks per pin
gpio_monitor: Allow multiple callbacks per pin

The currement implementation of the gpio_monitor allows only
one callback per pin.
This commit implements a more flexible gpio_monitor that can
manage up to 20 callbacks with no restriction on the number
of callbacks per pin.

Signed-off-by: Francois Berder <0eabc3e9da54407da074ac08d4217d54f5b94915@imgtec.com>

mtusnio/LetMeCreateIoT,mtusnio/LetMeCreateIoT,CreatorDev/LetMeCreateIoT,CreatorDev/LetMeCreateIoT,mtusnio/LetMeCreateIoT,CreatorDev/LetMeCreateIoT,CreatorDev/LetMeCreateIoT,mtusnio/LetMeCreateIoT