media: dvb-core: Kconfig: default to use dynamic minors

All modern Linux distributions nowadays use udev or some
alternative (like systemd). So, it makes sense to change
the default to use dynamic minors.

Please notice that this default doesn't enable any code.
It just changes the dvb-core behavior.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>