[ARM] Add asm/memory.h to asm/numnodes.h

Since the defintion of NODES_SHIFT may be overridden in asm/arch/memory.h
it's important to include asm/memory.h into asm/numnodes.h to ensure
that the correct value is always defined.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>