freeswitch: bump version to 1.8.1

freeswitch: bump version to 1.8.1

Enables openssl-1.1.x compatible compile.

- add tiff dependency (bundled tiff source is gone)
- rebase (and git format) 0001-libvpx-cross.patch patch
- update libs/srtp/LICENSE file hash (updated copyright year)

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
[Bernd:
- bumped to 1.8.1
- rebased patch 0001 to the tarball release
- added hashes for libvpx & libyuv license files]
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>