MIPS: Alchemy: rewrite USB platform setup.

Use runtime CPU detection to setup all USB parts.
Remove the Au1200 OTG and UDC platform devices since there are no
drivers for them anyway.
Clean up the USB address mess in the au1000 header.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
To: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/2703/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>