gpio: Add support for TPS68470 GPIOs

This patch adds support for TPS68470 GPIOs.
There are 7 GPIOs and a few sensor related GPIOs.
These GPIOs can be requested and configured as
appropriate.

The GPIOs are also provided with descriptive names.
However, the typical use case is that the OS GPIO
driver will interact with TPS68470 GPIO driver
to configure these GPIOs, as requested by the
platform firmware.

Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>