dvb: use runtime DVB_API_VERSION check

we cannot rely on a compiletime check, because
the linux-libc-headers we're building against
might differ from the actual kernel headers.
So first do a compiletime check for the availability
of defines and enums (in linux-libc-headers),
followed by a runtime check for the actual kernel
support (where applicable).
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2