pinctrl/u300/coh901: stop spawning pinctrl from GPIO

Let's stop spawning the pinctrl driver from the GPIO driver,
we have these two mechanisms broken apart now, and they can
each probe in isolation. If the GPIO driver cannot find its
pin controller (pinctrl-u300), the pin controller core will
tell it to defer probing.

Reviewed-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>