pinctrl: New driver for TI DA850/OMAP-L138/AM18XX pinconf

This adds a new driver for pinconf on TI DA850/OMAP-L138/AM18XX. These
SoCs have a separate controller for controlling pullup/pulldown groups.

Signed-off-by: David Lechner <david@lechnology.com>
Reviewed-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>