drm/amd/display: not reset dmub in driver.

[Why]
during S0i3, set power state is toggled a few times,
and dmub uC will restart with current reset/hw_init.

[How]
Remove reset in set power state, and before doing hw_init,
check if dmub is enabled, and doing FW autoload check only
if dmub is already enabled.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>