clock: implement a driver for the Tegra CAR

Implement a clock uclass driver for the Tegra CAR. This allows clients to
use standard clock APIs on Tegra. This device is intended to be
instantiated by the core Tegra CAR driver, rather than being instantiated
directly from DT. The implementation uses the existing custom Tegra-
specific clock APIs to avoid coupling the series with significant
refactoring of the existing Tegra clock/clock code. The driver currently
only supports peripheral clocks, and avoids support for other clocks such
as PLLs and external clocks. This should be sufficient to convert over all
Tegra peripheral drivers, and avoids a complex implementation which calls
different Tegra-specific clock APIs based on the type of clock being
manipulated.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>