Add ide-timing functionality to libata.

This is needed for full AMD and VIA drivers and possibly more. Functions
to turn actual clocking and cycle timings into register values. Also to
merge shared timings to compute an optimal timing set.

Built from the drivers/ide version by Vojtech Pavlik

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>