media: dvb: Clean-up capabilities of demux devices

demux kernel implementation exposed capabilities both to user-space
applications and internally to demux-device layer. demux-device
layer was changed to re-use the capabilities reported to user-space
to avoid duplications and redefinitions of capabilities.

Change-Id: Ib0eed8240c1bae0fce5ed7a1bae8129b185f3f87
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>