Input: imx_keypad - convert to a DT-only driver

i.MX has been converted to a DT-only platform, so make the
adjustments to the driver to convert it to a DT-only driver.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20210327194307.541248-1-festevam@gmail.com


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