Commit the common portion of FS#9708: ATA (IDE) DMA by Boris Gjenero with a couple...

Commit the common portion of FS#9708: ATA (IDE) DMA by Boris Gjenero with a couple cosmetic tweaks and without the inclusion of 'FS#9721: No error check after writes in ata.c'changes (which can be done separately). No code is changed for targets without HAVE_ATA_DMA defined other than to not display DMA modes in the View Disk Info debug screen if not using DMA (Gigabeat F/X/S were). No target uses the code yet but Gigabeat S use will follow shortly.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@20298 a1c6a512-1295-4272-9138-f99709370657