pinctrl: tegra: refactor probe handling

Rather than having a single tegra-pinctrl driver that determines whether
it's running on Tegra20 or Tegra30, instead have separate drivers for
each that call into utility functions to implement the majority of the
driver. This change is based on review feedback of the SPEAr pinctrl
driver, which had originally copied to Tegra driver structure.

This requires that the two drivers have unique names. Update a couple
spots in arch/arm/mach-tegra for the name change.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>