libata-core: Expose gtm methods for driver use

Talk to the dark side our driver has to, yes. Much misleading is the
data. Store it in a structure we do so that it may be parsed.

Signed-off-by: Alan Cox <alan@redhat.com>
--
Whats small, old and shouts phrases out of order across mountains ?
Yodla..
Signed-off-by: Jeff Garzik <jeff@garzik.org>