clk: tegra: pll: Simplify clk_enable_path

Instead of having multiple similar wrapper functions for
_clk_pll_[enable|disable], we can simplify it to single
wrappers and use checks to avoid the logic we don't want to use.

Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>