ide: factor out cable detection from ide_init_port()

* Factor out cable detection from ide_init_port() to ide_port_cable_detect().

* Move ide_port_cable_detect() call to ide_device_add_all().

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