sparc: Use device_type helpers to access the node type

Remove directly accessing device_node.type pointer and use the accessors
instead. This will eventually allow removing the type pointer.

Replace the open coded iterating over child nodes with
for_each_child_of_node() while we're here.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>