platform/x86: amd-pmc: Add support for logging s0ix counters

platform/x86: amd-pmc: Add support for logging s0ix counters

Even the FCH SSC registers provides certain level of information
about the s0ix entry and exit times which comes handy when the SMU
fails to report the statistics via the mailbox communication.

This information is captured via a new debugfs file "s0ix_stats".
A non-zero entry in this counters would mean that the system entered
the s0ix state.

If s0ix entry time and exit time don't change during suspend to idle,
the silicon has not entered the deepest state.

Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210629084803.248498-6-Shyam-sundar.S-k@amd.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>