dm: core: Modify default for OFNODE_MULTI_TREE

There is a preference to use the "ofnode" API for FDT fixups
moving forward.  The FDT fixup will usually be for the kernel FDT.  To
fixup the kernel FDT with the ofnode API, it's required to set the
OFNODE_MULTI_TREE option.

To ensure existing users of kaslr fdt fixup are not impacted, Let's modify
the default value for OFNODE_MULTI_TREE to ensure it's always set.
This will cause a 1007 byte increase in the code size.

Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
Reviewed-by: Simon Glass <sjg@chromium.org>