cpufreq/intel_pstate: Load only on Intel hardware

This driver is Intel-only so loading on anything which is not Intel is
pointless. Prevent it from doing so.

While at it, correct the "not supported" print statement to say CPU
"model" which is what that test does.

Fixes: 076b862c (cpufreq: intel_pstate: Add reasons for failure and debug messages)
Suggested-by: Erwan Velu <e.velu@criteo.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>