drm/amd/display: Power down hw blocks on boot

[WHY]
On headless boot a DIG may be turned on by VBIOS on RN.  This leads to
display_count being non-zero in hybrid graphics cases leading to SMU
DISPLAY_OFF message not being sent.

[HOW]
Power down hardware on boot
if seamless boot is not occurring
(power_down_display_on_boot == 1)

Signed-off-by: Sung Lee <sung.lee@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>