drm/amd/display: increase MAX_SURFACES to the value supported by hw

As the hw supports up to 4 surfaces, increase the maximum number of
surfaces to prevent the DC error when trying to use more than three
planes.

[drm:dc_state_add_plane [amdgpu]] *ERROR* Surface: can not attach plane_state 000000003e2cb82c! Maximum is: 3

Link: drm/amd#3693


Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>