platform/x86/amd: pmc: Add an extra STB message for checking s2idle entry

The `check` callback is run right before the cores are put into HLT.
This will allow checking synchronization problems with other software
that writes into the STB.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20220829162953.5947-5-mario.limonciello@amd.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>