Add support to Sunix serial boards with up to 16 ports.

Sunix board need its own setup callback instead of using Timedia's, to
properly support more than 4 ports.

Cc: Morris Ku <morris_ku@sunix.com>
Cc: Debbie Liu <debbie_liu@sunix.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Link: https://lore.kernel.org/r/20190809190130.30773-1-kai.heng.feng@canonical.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>