hwpstate_amd(4): Add knobs to get/set all fields of CPPC_REQUEST

This will allow experimentations and finer-grained tuning to the full
extent allowed by the hardware, which is especially important given that
the spec leaves to hardware implementors an important leeway in
interpreting CPPC's numeric parameters, causing the same settings to
have different effects on different CPU models.

PR: 292615
Reviewed by: aokblast (older version)
Relnotes: yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55010