[libata] conversion to new debug scheme, part 1 of $N

The first 25% of libata-core.c converted to the new debugging scheme.

Signed-off-by:  <petkov@math.uni-muenster.de>

(with addition of ATA_MSG_WARN to standard msg_enable by me)
Signed-off-by: Jeff Garzik <jeff@garzik.org>