V4L/DVB (12423): cxusb, d680 dmbth use unified lgs8gxx code instead of lgs8gl5

Use unified lgs8gxx frontend instead of reverse engineered lgs8gl5 frontend.
After this patch, lgs8gl5 frontend could be mark as deprecated.
Future development should base on unified lgs8gxx frontend.

Signed-off-by: David T.L. Wong <davidtlwong@gmail.com>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>