Comment # 1 on bug 1200254 from Takashi Iwai

OK, both CONFIG_NET_DSA_REALTEK_SMI or _MDIO depend on CONFIG_OF, which isn't
the case for x86.  So we can disable CONFIG_NET_DSA_REALTEK_RTL* on x86, too.

I updated the config for x86_64 now.  Thanks for the report.