pinctrl: remove bindings for pinconf options needing more thought

Some options currently take arguments in unspecified driver-specific units.
As pointed out by Stephen Warren, driver specific values should not be part
of generic devicetree bindings describing the hardware.

Therefore remove the critical bindings again, before they become part of
an official release.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>