vlc: fix live555 support

vlc looks for a *.pc file which is not provided by the live555 package.
So, instead, we explicitly set the LIVE555_CFLAGS and LIVE555_LIBS
variables.

Fixes:
  http://autobuild.buildroot.org/results/b59/b5972ecad4e5004dc23a2366066ce45346994f58/build-end.log



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>