drm/amd/display: Set number of pipes to 1 if the second pipe was disabled

[why]
Some ODM-related register settings are inconsistently updated by VBIOS, causing
the state in DC to be invalid, which would then end up crashing in certain
use-cases (such as disable/enable device).

[how]
Check the enabled status of the second pipe when determining the number of
OPTC sources. If the second pipe is disabled, set the number of sources to 1
regardless of other settings (that may not be updated correctly).

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>