libata: ignore SIMG4726 config pseudo device

I was hoping ATA_HORKAGE_NODMA | ATA_HORKAGE_SKIP_PM could keep it
happy but no even this doesn't work under certain configurations and
it's not like we can do anything useful with the cofig device anyway.
Replace ATA_HORKAGE_SKIP_PM with ATA_HORKAGE_DISABLE and use it for
the config device.  This makes the device completely ignored by
libata.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>