pinctrl: add a Gemini SoC pin controller

This adds a pin control (only multiplexing) driver for the Gemini
SoC so we can sort out this complex platform in an orderly manner.

This driver will detect the chip/package version as SL3512 or SL3516
(also known as CS3512 and CS3516 etc) and register the apropriate
pin set.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>