mxf: Detect Vanc/Vbi SMPTE-436M mxf track

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
mxf: Extract origin information from material and source track

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
configure: Use require_pkg_config for Speex

Distributors and integrators nowadays have less problems by leveraging
pkg-config files than having to set custom CFLAGS and LDFLAGS.