MIPS: Alchemy: sleepcode without compile-time cputype dependencies

Split the low-level sleepcode into per-cpu functions instead of
relying on compile-time-defined cpu type.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
To: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: http://patchwork.linux-mips.org/patch/1281/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>