ata: do some threading-related corrections (some sync related where it matters)....

ata: do some threading-related corrections (some sync related where it matters). Make sure 'sleeping' is 'false' before the powerup sequence (throws-off powermgmt and it *is* about to woken again and powermgmt will need to compensate). Avoid looking at mutex flag directly; there's no tangible benefit I can discern and changes to the kernel that alter the meaning shouldn't be able to break anything. For that, in the jz sd driver, have sd_disk_is_active just return 'false' like all the other SD drivers do. If it *must* return this, it should implement it's own method but it seems to not matter.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26234 a1c6a512-1295-4272-9138-f99709370657