cpufreq: Tegra: implement intermediate frequency callbacks

cpufreq: Tegra: implement intermediate frequency callbacks

Tegra has been switching to intermediate frequency (pll_p_clk) forever.
CPUFreq core has better support for handling notifications for these
frequencies and so we can adapt Tegra's driver to it.

Also do a WARN() if clk_set_parent() fails while moving back to pll_x
as we should have atleast restored to earlier frequency on error.

Tested-by: Stephen Warren <[email protected]>
Signed-off-by: Viresh Kumar <[email protected]>
Reviewed-by: Doug Anderson <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>