cpufreq: powernow-k8: Re-order the init checks

The powernow-k8 driver will do checks at startup that the current
active driver is acpi-cpufreq and show a warning when they're not
expected.

Because of this the following warning comes up on systems that
support amd-pstate and compiled in both drivers:
`WTF driver: amd-pstate`

The systems that support powernow-k8 will not support amd-pstate,
so re-order the checks to validate the CPU model number first to
avoid this warning being displayed on modern SOCs.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>