show_mem() was not correctly handling holes in the memory
map.  It was treating the freed sections of the map as
though they contained valid struct page entries.  This
could cause incorrect debugging output or even a kernel
panic.

This patch keeps the struct meminfo around after system
initialization so that show_mem() can use it when
scanning memory.  show_mem() now walks over each bank
of each online node, rather than assuming that each node
contains a single contiguous bank.
Signed-off-by: Ray Lehtiniemi <rayl@mail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>