cpufreq: intel_pstate: Broxton support

Add Broxton CPU model number.

Broxton requires core_params to get performance limits via MSRs, but
it is an Atom platform, which requires more power optimized algorithm.

So the P state selection will use similar algorithm as other Atom
platforms.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>