Input: pxa27x-keypad - drop support for platform data

There are no in-kernel users of pxa27x_keypad_platform_data in the
kernel, and the driver supports configuration via device tree, so drop
support of static platform data and move properties parsing from
OF-specific methods to generic ones.

Link: https://lore.kernel.org/r/20250817215316.1872689-3-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: dtor