gayle: set IDE_HFLAG_SERIALIZE explictly

If IDE doubler is used ports need to be serialized.  Currently
init_irq() handles it fine but lets also set IDE_HFLAG_SERIALIZE
host flag explicitly in preparation for future changes.

Also convert the driver to use struct ide_port_info while at it.

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>