gstreamer1.0-plugins: disable introspection on mips64

gstreamer1.0-plugins: disable introspection on mips64

The failure is weird and difficult to diagnoze, so disable the
introspection for now:

qemu-mips64: error while loading shared libraries: .../recipe-sysroot/usr/lib/libgthread-2.0.so.0: ELF file data encoding not little-endian

Note that it shows up only for one specific library (gstaudio), and only
on mips64. Introspection data for other libraries is generated just fine.

Signed-off-by: Alexander Kanavin <alexander.kanavin@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>