lmb: Make lmb debugging more useful.

Having to muck with the build and set DEBUG just to
get lmb_dump_all() to print things isn't very useful.

So use pr_info() and use an early boot param
"lmb=debug" so we can simply ask users to reboot
with this option when we need some debugging from
them.

Signed-off-by: David S. Miller <davem@davemloft.net>