package/tvheadend: add option to en-/disable transcoding support

package/tvheadend: add option to en-/disable transcoding support

https://github.com/tvheadend/tvheadend/commit/014bb9505e1d7eb6e37e10931dd89ab3b1a0dc01
extended the already present transcoding support and included vaapi-
accelerated transcoding.

In order to support these new options and their numerous dependencies
we add a new Kconfig option for transcoding support to allow users to
disable transcoding support, because they use tvheadend for recording
or by its internal hts protocol, for example with the kodi-pvr-hts
addon.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>