MIPS: Alchemy: Au1300 SoC support

Add basic support for the Au1300 variant(s):
- New GPIO/Interrupt controller
- DBDMA ids
- USB setup
- MMC support
- enable various PSC drivers
- detection code.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2866/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>