[POWERPC] New registration for common Xilinx Virtex ppc405 platform devices

Currently virtex support in mainline make use of the infrastructure in
arch/ppc/syslib/ppc_sys.c for registering common devices on virtex ppc405
platforms.  The ppc_sys.c code is not well suited to the dynamic nature of
FPGA designs and makes adding new board ports more complex.  This patch
adds a new listing of common devices which does not depend on the ppc_sys.c
infrastructure.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Paul Mackerras <paulus@samba.org>