[CPUFREQ] Powernow-k8: support family 0xf with 2 low p-states

Provide support for family 0xf processors with 2 P-states
below the elevator voltage.  Remove the checks that prevent
this configuration from being supported and increase the
transition voltage to prevent errors during the transition.

Signed-off-by: Mark Langsdorf <mark.langsdorf@amd.com>
Signed-off-by: Dave Jones <davej@redhat.com>