x86: intel_epb: Allow model specific normal EPB value

The current EPB "normal" is defined as 6 and set whenever power-up EPB
value is 0. This setting resulted in the desired out of box power and
performance for several CPU generations. But this value is not suitable
for AlderLake mobile CPUs, as this resulted in higher uncore power.
Since EPB is model specific, this is not unreasonable to have different
behavior.

Allow a capability where "normal" EPB can be redefined. For AlderLake
mobile CPUs this desired normal value is 7.

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