Input: stmpe-keypad - add support for Device Tree bindings

This patch allows the STMPE driver to be successfully probed and
initialised when Device Tree support is enabled. Besides the usual
platform data changes, we also separate the process of filling in
the 'in use' pin bitmap, as we have to extract the information from
Device Tree in the DT boot case.

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