clk: tegra: Export peripheral reset functions

The tegra_periph_reset_assert() and tegra_periph_reset_deassert()
functions can be used by drivers to reset peripherals. In order to allow
such drivers to be built as modules, export the functions.

Note that this restores the status quo as the functions were exported
before the move to the drivers/clk tree.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>