ide: move ack_intr() method into 'struct ide_port_ops' (take 2)

Move the ack_intr() method into 'struct ide_port_ops', also renaming it to
test_irq() while at it...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>