sparc32: fix sparse "Should it be static?" in mm/

Fix following warnings:
srmmu.c:870:13: warning: symbol 'srmmu_paging_init' was not declared. Should it be static?
iommu.c:430:13: warning: symbol 'ld_mmu_iommu' was not declared. Should it be static?
leon_mm.c:21:5: warning: symbol 'srmmu_swprobe_trace' was not declared. Should it be static?

Add proper prototypes or define static to fix them.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>