cpufreq: cpu0: OPPs can be populated at runtime

OPPs can be populated statically, via DT, or added at run time with
dev_pm_opp_add().

While this driver handles the first case correctly, it would fail to populate
OPPs added at runtime. Because call to of_init_opp_table() would fail as there
are no OPPs in DT and probe will return early.

To fix this, remove error checking and call dev_pm_opp_init_cpufreq_table()
unconditionally.

Update bindings as well.

Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
Tested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>