Input: stmpe - enforce device tree only mode

The STMPE keypad controller is only used with device tree configured
systems, so force the configuration to come from device tree only, and now
actually get the rows and cols from the device tree too.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>