MIPS: mark prom_free_prom_memory() everywhere with __init

On OCTEON the function is non-trivial and we can potentially even save
some memory.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9338/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --cc arch/mips/cavium-octeon/setup.c
Simple merge

diff --cc arch/mips/lantiq/prom.c
Simple merge

diff --cc arch/mips/mti-sead3/sead3-init.c
Simple merge