of: merge of_node_get(), of_node_put() and of_find_all_nodes()

Merge common code between Sparc, PowerPC and Microblaze.

Sparc differs in the implementation at this point, so this patch uses
a #ifdef to handle sparc differently for now.  The merging of
implementations will occur in a later patch

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Michal Simek <monstr@monstr.eu>
Acked-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>