cpufreq: dt: Add support for turbo/boost mode

With opp-v2 DT bindings, few OPPs can be used only for the boost mode.
But using such OPPs require the boost mode to be supported by cpufreq
driver.

We will parse DT bindings only during ->init() and so can enable boost
support only after registering cpufreq driver.

This enables boost support as soon as any policy has boost/turbo OPPs
for its CPUs.

We don't need to disable boost support as that is done by the core, when
the driver is unregistered.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>