buildroot

mediastreamer: add dependency on host-vim

host-vim is needed to provide the xxd tool, otherwise the build fails
with:

checking for xxd... no
configure: error: "xxd is required (provided by vim package)"

This isn't noticed by the autobuilders, presumably because all of them
have vim installed locally.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>