MIPS: Increase range of CONFIG_FORCE_MAX_ZONEORDER

There is nothing that prevents us from using lower maximum values.
It's something that we actually want, when using bigger page sizes on
devices with low RAM.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>