ahci: make NO_NCQ handling more consistent

ahci_save_initial_config() is responsible for reading, screening the
host CAP register and storing the modified result into hpriv->cap for
the rest of the driver.  Move ATA_FLAG_NO_NCQ handling into
ahci_save_initial_config().  It's more consistent this way and the
rest of the driver can always refer to hpriv->cap to determine
configured capability.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>