qcom: replace split SC7180 venus firmware images with symlink

qcom: replace split SC7180 venus firmware images with symlink

Qualcomm drivers have supported non-split firmware since since 2019 in
linux kernel commit 498b98e93900 ("soc: qcom: mdt_loader: Support
loading non-split images").  The firmware loader works with either the
split or non-split firmware types. The venus driver for SC7180 currently
loads venus.mdt, not the unified venus.mbn.

This commit removes the non-split images. It adds a link from venus.mdt
to venus.mbn. This retains existing driver compatibility, while gaining
the benefit of reducing size of the deployed files.

I verified this change with on ChromeOS using kernels based on 5.4 and
5.15.

Signed-off-by: Nathan Hebert <nhebert@chromium.org>