cpufreq/amd-pstate: Push adjust_perf vfunc init into cpu_init

cpufreq/amd-pstate: Push adjust_perf vfunc init into cpu_init

As the driver can be changed in and out of different modes it's possible
that adjust_perf is assigned when it shouldn't be.

This could happen if an MSR design is started up in passive mode and then
switches to active mode.

To solve this explicitly clear `adjust_perf` in amd_pstate_epp_cpu_init().

Tested-by: Klara Modin <klarasmodin@gmail.com>
Tested-by: Dhananjay Ugwekar <dhananjay.ugwekar@amd.com>
Link: https://lore.kernel.org/r/20241028145542.1739160-1-superm1@kernel.org
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>