Input: lpc32xx-keys - select INPUT_MATRIXKMAP

This adds a "select" dependency of KEYBOARD_LPC32XX on INPUT_MATRIXKMAP,
as the other drivers are doing in this regard. This fixes the following
compile error if KEYBOARD_LPC32XX is enabled but INPUT_MATRIXKMAP is not:

drivers/input/keyboard/lpc32xx-keys.c:230: undefined reference to
`matrix_keypad_build_keymap'

Signed-off-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>