Input: maple_keyb - implement open and close methods

Instead of polling the keyboard constantly from probe, implement open
and close methods for the input device to only start polling when the
device is actually opened by userspace, and stop polling when it is
closed.

This matches the behavior of maplemouse and maplecontrol drivers.

Assisted-by: Antigravity:gemini-3.5-flash
Link: https://patch.msgid.link/20260703-b4-maple-cleanup-v1-7-41e424964da5@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>