ide: Add tx4939ide driver (v6)

This is the driver for the Toshiba TX4939 SoC ATA controller.

This controller has standard ATA taskfile registers and DMA
command/status registers, but the register layout is swapped on big
endian.  There are some other endian issue and some special registers
which requires many custom dma_ops/tp_ops routines and build_dmatable.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: ralf@linux-mips.org
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>