drm/msm/dpu: Remove num_enc from topology struct in favour of num_dsc

Downstream calls this num_enc yet the DSC patches introduced a new
num_dsc struct member, leaving num_enc effectively unused.

Fixes: 7e9cc175

 ("drm/msm/disp/dpu1: Add support for DSC in topology")
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/515688/
Link: https://lore.kernel.org/r/20221221231943.1961117-7-marijn.suijten@somainline.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>