pinctrl: tegra20: Provide CDEV1/2 clock muxes

Muxing of pins MCLK1/2 determine the muxing of the corresponding clocks.
Make pinctrl driver to provide clock muxes for the CDEV1/2 pingroups, so
that main clk-controller driver could get an actual parent clock for the
CDEV1/2 clocks.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Marcel Ziswiler <marcel@ziswiler.com>
Tested-by: Marcel Ziswiler <marcel@ziswiler.com>
Tested-by: Marc Dietrich <marvin24@gmx.de>
Acked-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>