When the OF code was originally made common by Grant in commit
51975db0 ("of/flattree: merge early_init_dt_scan_memory() common
code") (Feb 2010), the common code inherited a hack to handle
PPC "longtrail" machines, which had a "memory@0" node with no
device_type.

That check was then made to only apply to PPC32 in b44aa25d ("of:
Handle memory@0 node on PPC32 only") (May 2014).

But according to Paul Mackerras the "longtrail" machines are long
dead, if they were ever seen in the wild at all. If someone does still
have one, we can handle this firmware wart in powerpc platform code.

So remove the hack once and for all.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Rob Herring <robh@kernel.org>