[POWERPC] 86xx: Add device tree source for Wind River SBC8641D

This adds in the device tree source for the SBC8641D, based
largely on the mpc8641_hpcn.dts.  The biggest differences are
the lack of a complex IRQ mapping (since no Uli/i8259 cascade)
and the different layout of devices on the localbus node.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>