cpufreq: intel_pstate: Clear HWP desired on suspend/shutdown and offline

Commit a365ab6b ("cpufreq: intel_pstate: Implement the
->adjust_perf() callback") caused intel_pstate to use nonzero HWP
desired values in certain usage scenarios, but it did not prevent
them from being leaked into the confugirations in which HWP desired
is expected to be 0.

The failing scenarios are switching the driver from the passive
mode to the active mode and starting a new kernel via kexec() while
intel_pstate is running in the passive mode.

To address this issue, ensure that HWP desired will be cleared on
offline and suspend/shutdown.

Fixes: a365ab6b ("cpufreq: intel_pstate: Implement the ->adjust_perf() callback")
Reported-by: Julia Lawall <julia.lawall@inria.fr>
Tested-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>