gpio: tc3589x: get rid of platform data

This device is only used from the device tree, and the startup()
and remove() callbacks are not used anywhere in the kernel, so
retire them and the pdata altogether.

Cc: Samuel Ortiz <sameo@linux.intel.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>