[POWERPC] Fix booting on Momentum "Apache" board (a Maple derivative)

This extends the maple device-tree workarounds to work on the
Apache board as well, and extends the maple platform probing code
to recognize the Apache board.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>