sparc,leon: Redefine MMU register access asi if CONFIG_LEON

SPARC-LEON has a different ASI for mmu register accesses.

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