packaging: debian: use cross compilation for armhf platforms

Using qemu in user mode to build jami package for raspbian platforms
adds a lot of overhead.

Remove the virtualization using the Debian 10 cross-compiling toolchain.
The target platform (i.e. the platform on which the package will be
installed) has to be set and some compilation options has to be added in
the debian/rules file.

Also add the armhf architecture in the Docker container in order to
install the package dependencies for this platform.

Change-Id: Ic2282ad9377d52482bca4a4f0ef017fbcc1f8eb7