[libata] sata_mv: minor cleanups

* trim trailing whitespace
* document some flags, registers, and register bits
* fix locking around EDMA on/off and configuration
* continue replacing "constant OP var" with "var OP constant"
* use new pci_try_set_mwi()

Signed-off-by: Jeff Garzik <jeff@garzik.org>
1 file changed