qcom/vpu-1.0: drop split firmware in favour of the mbn file

Follow the example of the sc7280 and sc7180 (venus-5.4, vpu-2.0) and
drop the split firmare files (mdt + bNN) in favour of using the squashed
mbn file.  For backwards compatibility generate the mdt -> mbn symlink.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>