drm/amd/display: Remove duplicate dm_pp_power_level enum

This is really just a copy of dm_pp_clocks_state, so just use that one.

Thanks to Matthias Kaehlke for spotting this.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>