cpufreq/amd-pstate: Overhaul locking

cpufreq/amd-pstate: Overhaul locking

amd_pstate_cpu_boost_update() and refresh_frequency_limits() both
update the policy state and have nothing to do with the amd-pstate
driver itself.

A global "limits" lock doesn't make sense because each CPU can have
policies changed independently.  Each time a CPU changes values they
will atomically be written to the per-CPU perf member. Drop per CPU
locking cases.

The remaining "global" driver lock is used to ensure that only one
entity can change driver modes at a given time.

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>