sunxi: prevent mali drivers from building every time

This patch was suggested to prevent the mali drivers from rebuild
every time the modules are built.  It simply creates symlinks to
sources used by both ump.ko and mali.ko so that their objects are built
in separate directories; otherwise, there is a ping-pong effect between
the ump.ko objects and mali.ko objects overwriting each other.

Signed-off-by: Patrick Wood <patrickhwood@gmail.com>