media: media/frontend.h.rst.exceptions: add exceptions for new dvb defines

After some dvb/frontend.h additions, building the documentation
gives lots of warnings. Add the missing pieces to
frontend.h.rst.exceptions.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>