soc/amd/phoenix: introduce and use pstate_msr bitfield struct

soc/amd/phoenix: introduce and use pstate_msr bitfield struct

Add the pstate_msr union of a bitfield struct and a raw uint64_t to
allow easier access of the bitfields of the P state MSRs and use this
bitfield struct in get_pstate_core_freq and get_pstate_core_power. The
signature of those two function will be changed in a follow-up commit.
PPR #57019 Rev 1.65 and PPR #57396 Rev 1.54 were used as a reference as
well as the reference code. This patch also adds and uses the cpu_vid_8
bit which is the 9th bit of the voltage ID specified in the SVI3 spec.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ia024d32ae75cf2ffbc2a2e86a8b3af3dc6cbad61
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73923
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>