Turns out distros always enabled burst mode and it is pretty essential so
do the same. Also sort out the post DMA mode restore properly.

My 20263 card now seems happy but needs some four drive tests done yet
(when I've persuaded the kernel not to hang in the edd boot code if I
plug them in ..)
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>