cpufreq / intel_pstate: Fix intel_pstate_init() error path

If cpufreq_register_driver() fails just free memory that has been
allocated and return. intel_pstate_exit() function is removed since we
are built-in only now there is no reason for a module exit procedure.

Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
cpufreq / intel_pstate: Do not load on VM that does not report max P state.

It seems some VMs support the P state MSRs but return zeros. Fail
gracefully if we are running in this environment.

References: https://bugzilla.redhat.com/show_bug.cgi?id=916833
Reported-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>