package/freeswitch: new package

package/freeswitch: new package

This commit adds freeswitch without any configured modules and with a
minimal set of non-optional dependencies. All other dependencies and
modules will be added by further patches in this series.

Please note that freeswitch source repo bundles some libraries which
are also available as buildroot packages. The freeswitch build system
does not allow to use system libraries in these cases:

  apr, apr-util, libsrtp, libvpx, libyuv, sofia-sip, tiff

The reason are patches to these packages by the freeswitch project
which are not yet upstream. There is an open JIRA report for this
situation:
https://freeswitch.org/jira/si/jira.issueviews:issue-html/FS-353/FS-353.html

More historic infos can be found here:
http://article.gmane.org/gmane.comp.telephony.freeswitch.devel/2715
https://freeswitch.org/the-missing-link/

In the 1.6.7 version bump libvpx & libyuv were also moved in-tree:
https://freeswitch.org/stash/projects/FS/repos/freeswitch/commits/febe0f8dacea2d2a31902b3dc469be757f8c3c4d
https://freeswitch.org/stash/projects/FS/repos/freeswitch/commits/44da905b4f6b3b35e94b4948fb70dec7b5071ded

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>