sparc32,leon: move leon mmu functions to leon_mm.c

We already have a leaon specific file - so
keep all the laon stuff in one place.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Konrad Eisele <konrad@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>