cpufreq: intel_pstate: Document hybrid processor support

Describe the support for hybrid processors in intel_pstate, including
the CAS and EAS support, in the admin-guide documentation.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/1935040.CQOukoFCf9@rjwysocki.net