Instead of being OF-specific, let's switch to using generic device
properties, which will make this code usable on ACPI, device tree and
legacy boards that use property sets.

As part of the change let's rename matrix_keypad_parse_of_params() to
matrix_keypad_parse_properties().
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>