gpio: Add driver for TI TPIC2810

Add driver for TI TPIC2810 8-Bit LED Driver with I2C Interface.

The TPIC2810 has 8 open-drain outputs that can but used to drive
LEDs and other low-side switched resistive loads.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>