drm/amd/pm: Use pm_display_cfg in legacy DPM (v2)

drm/amd/pm: Use pm_display_cfg in legacy DPM (v2)

This commit is necessary for DC to function well with chips
that use the legacy power management code, ie. SI and KV.
Communicate display information from DC to the legacy PM code.

Currently DC uses pm_display_cfg to communicate power management
requirements from the display code to the DPM code.
However, the legacy (non-DC) code path used different fields
and therefore could not take into account anything from DC.

Change the legacy display code to fill the same pm_display_cfg
struct as DC and use the same in the legacy DPM code.

To ease review and reduce churn, this commit does not yet
delete the now unneeded code, that is done in the next commit.

v2:
Rebase.
Fix single_display in amdgpu_dpm_pick_power_state.

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