intel_pstate: skip scheduler hook when in "performance" mode

intel_pstate: skip scheduler hook when in "performance" mode

When the governor is set to "performance", intel_pstate does not
need the scheduler hook for doing any calculations.  Under these
conditions, its only purpose is to continue to maintain
cpufreq/scaling_cur_freq.

The cpufreq/scaling_cur_freq sysfs attribute is now provided by
shared x86 cpufreq code on modern x86 systems, including
all systems supported by the intel_pstate driver.

So in "performance" governor mode, the scheduler hook can be skipped.
This applies to both in Software and Hardware P-state control modes.

Suggested-by: Srinivas Pandruvada <[email protected]>
Signed-off-by: Len Brown <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>