drivers: gpio: davinci: Match GPIO address with Linux

Currently, the Zephyr dt requires address to the direction register
instead of the base GPIO address. usually means base address + 0x10 when
compared with Linux.

To make things more consistent between linux and zephyr, handle the
direction offset in the driver itself. This also lays the foundation for
supporting more than 32 GPIOs per port in the future by introducing
offsets for all the banks.

Signed-off-by: Ayush Singh <ayush@beagleboard.org>