Put v4l2_codec2 underneath a soong namespace

It isn't currently possible for multiple soong modules in the same build
to define the same output path, even if one overrides another, so given
that the contract of codec2 involves loading libraries from some
specific paths, these paths must not have modules built into them by
default or they can not be overridden by other soc_specific code.

Change-Id: I4823f9942d69a29c53ed88c5e39c3b0cb0786973
Test: Build device using v4l2_codec2 from installclean and ensure the output has not changed
Bug: 200265668