MIPS: Alchemy: devboards: kill prom.c

move contents to already existing platform.c file.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3287/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>