MIPS: Alchemy: Cleanup DMA addresses

According to the databooks, the Au1000 DMA engine must be programmed with
the physical FIFO addresses.  This patch does that; furthermore this
opened the possibility to get rid of a lot of now unnecessary address
defines.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
To: Linux-MIPS <linux-mips@linux-mips.org>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Patchwork: https://patchwork.linux-mips.org/patch/2348/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org