[POWERPC] 86xx: Add support for Wind River SBC8641D board

This adds support for the Wind River SBC8641D board, based
largely on the mpc86xx_hpcn support.  The biggest difference is
the lack of the Uli and the i8259 cascade, which simplifies things.

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