Input: pxa27x-keypad - use matrix_keymap for matrix keys

pxa27x-keypad includes matrix keys. Make use of matrix_keymap
for the matrix keys.

Signed-off-by: Chao Xie <chao.xie@marvell.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>