Read all of the OF memory and translation tables, then read
the physical available memory list twice.

When making these requests, OF can allocate more memory to
do it's job, which can remove pages from the available
memory list.

So fetch in all of the tables at once, and fetch the available
list last to make sure we read a stable value.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>