drm/amd/pm/smu7: Notify SMU7 of DC->AC switch

drm/amd/pm/smu7: Notify SMU7 of DC->AC switch

When ATOM_PP_PLATFORM_CAP_HARDWAREDC is set,
the SMU has a GPIO pin for detecting AC/DC switch
and everything works automatically.

Otherwise when there is no GPIO pin, the SMU can
automatically detect switching to DC, but needs
to be notified of switching to AC.

Use PPSMC_MSG_RunningOnAC to notify the SMC
when switching to AC.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>