drm/amd/display: Change dc_set_power_state() to bool instead of int

DC code is reused by other OSes and so Linux return codes don't
make sense.  Change dc_set_power_state() to boolean and add a wrapper
dm_set_power_state() to return a Linux error code for the memory
allocation failure.

Suggested-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>