[POWERPC] Remove dtc build cruft from DTS files

The patch below removes the dtc incantation instructions from the
in-kernel DTS files.  It's not needed, and is prone to being
out-of-date most of the time.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>