MIPS: Alchemy: merge GPR/MTX-1/XXS1500 board code into single files

Most of these files are have more comments than real code;  merge
them all into single board-<name>.c files.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2869/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>