drm/amd/display: update max streams per surface

drm/amd/display: update max streams per surface

Increse to 6 as that is the max surfaces supported asics can have.
The is no practical use case yet, but this is valuable for pre-si
validation.

Reviewed-by: Ariel Bernstein <Eric.Bernstein@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>