Input: stmpe - bias keypad columns properly

All keypad column pins used as inputs should be pulled up on the STMPE24xx,
but this is not done by the current driver.  Add some logic that will do
this properly. The STMPE1601 also has a keypad controller, but explicitly
does *NOT* require you to set up any pull-ups.

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