memblock: Improve debug output when resizing the reserve array

Print out the location info in addition to which array is being
resized. Also use memblocK_dbg() to put that under control of
the memblock_debug flag.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>