drivers: gpio: davinci: Add pinctrl

Add pinctrl to the Davinci GPIO driver to allow muxing pins dirctly
in this driver.

Also aligned the macro backslashes as line continuation character at
the end of each line with each at the same position and removed the
GPIO_DAVINCI_DEVICE_INIT macro which seems to be not used.

Signed-off-by: Daniel Schultz <d.schultz@phytec.de>