This patch adds support for sil_3131 and sil_3531.  Both are
identical to 3124 except that they have only one port.  Bits 30 and 31
of ata_port_info->host_flags is used to encode available port numbers.
Version number is bumped to 0.22.

Edward Falk supplied all the necessary information and preliminary
patch.
Signed-off-by: NTejun Heo <htejun@gmail.com>