drm/amd/display: Set default ABM level to module parameter

drm/amd/display: Set default ABM level to module parameter

[Why]
The module parameter to specify the default ABM level is now defined,
so hook it up in DM.

[How]
On connector reset specify the default level. DC will program this as
part of the modeset since it gets passed onto the stream in
dm_update_crtc_state.

It's only set for eDP connectors, but it doesn't matter if this is
specified for connectors or hardware that doesn't support ABM.

It's DC's responsibility to check that ABM can be set or adjusted, and
DC does check that the DMCU firmware is running and if there's backlight
control available.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: David Francis <david.francis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>