Input: atmel_mxt_ts - support capacitive keys

Add support for touch keys found in some Atmel touch controller
configurations.

Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: André Apitzsch <git@apitzsch.eu>
Link: https://lore.kernel.org/r/20230407-atmel_keys-v2-2-92446a4343cb@apitzsch.eu


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