net: dsa: realtek: don't default Kconfigs to y

We generally default the vendor to y and the drivers itself
to n. NET_DSA_REALTEK, however, selects a whole bunch of things,
so it's not a pure "vendor selection" knob. Let's default it all
to n.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>