of/sparc: Remove sparc-local declaration of allnodes and devtree_lock

Both allnodes and devtree_lock are defined in common code.  The
extern declaration should be in the common header too so that the
compiler can type check.  allnodes is already in of.h, but
devtree_lock should be declared there too.

This patch removes the SPARC declarations and uses decls in of.h instead.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Michal Simek <monstr@monstr.eu>
Acked-by: David S. Miller <davem@davemloft.net>