drm/amd/display: Acquire DSC during split stream for ODM only if top_pipe

[WHY]
DSC should only be acquired per OPP. Therefore, DSC should only
be acquired for the top_pipe when ODM is enabled.
Not doing this check may lead to acquiring more DSC's than needed
when doing MPO + ODM Combine.

[HOW]
Only acquire DSC if pipe is top_pipe.

Signed-off-by: Sung Lee <sung.lee@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>