drm/amd/display: Exit IPS w/ DC helper for all dc_set_power_state cases

drm/amd/display: Exit IPS w/ DC helper for all dc_set_power_state cases

[why & how]
On D3 path during dc_set_power_state, we may be in idle_allowed=true,
at which point we will exit idle via dc_wake_and_execute_dmub_cmd_list
which doesn't update dc->idle_optimizations_allowed to false. This
would cause any future attempts to allow idle optimizations via the DC
helper to get skipped because the value is stale and not reflective of
the actual HW state.

Move dc_exit_ips_for_hw_access() to the top of the function.
Additionally ensure that dc_power_down_on_boot thread holds the DC
lock and only runs if there are 0 streams.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Ovidiu Bunea <ovidiu.bunea@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>