Input: bu21013_ts - convert to use GPIO descriptors

Input: bu21013_ts - convert to use GPIO descriptors

This driver can use GPIO descriptors rather than GPIO numbers
without any problems, convert it. Name the field variables after
the actual pins on the chip rather than the "reset" and "touch"
names from the devicetree bindings that are vaguely inaccurate.

No in-tree users pass GPIO numbers in platform data so drop
this. Descriptor tables can be used to get these GPIOs from a board
file if need be.

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