serial: tegra: use reset framework

Tegra's clock driver now provides an implementation of the common
reset API (include/linux/reset.h). Use this instead of the old Tegra-
specific API; that will soon be removed.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Thierry Reding <treding@nvidia.com>