sata_mv: optimize use of mv_edma_cfg

Try and avoid unnecessary reconfiguration of the EDMA config register
on every single non-EDMA I/O operation, by moving the call to
mv_edma_cfg() into mv_stop_edma().  It must then also be invoked
from mv_hardreset() and from mv_port_start().

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>