cpufreq/amd-pstate-ut: Allow lowest nonlinear and lowest to be the same

Several Ryzen AI processors support the exact same value for lowest
nonlinear perf and lowest perf.  Loosen up the unit tests to allow this
scenario.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: Dhananjay Ugwekar <dhananjay.ugwekar@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>