MIPS: Alchemy: remove no longer used au1xxx_ide.h header

Since the only user of this header (au1xxx-ide IDE host driver) is
now gone it can also be removed.

Acked-by: Paul Burton <paulburton@kernel.org>
Acked-by: Manuel Lauss <manuel.lauss@gmail.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>