gpio: sx150x: move platform data into driver

The sx150x has some platform data definition in <linux/i2c/sx150x.h>
but this file is only included from the driver in the whole kernel
so move its contents into the driver.

Cc: Wei Chen <Wei.Chen@csr.com>
Cc: Peter Rosin <peda@axentia.se>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>