sh: pretty print virtual memory map on boot.

This cribs the pretty printing from arch/x86/mm/init_32.c to dump the
virtual memory layout on boot. This is primarily intended as a debugging
aid, given that the newer CPUs have full control over their address space
and as such have little to nothing in common with the legacy layout.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>