powerpc/85xx: Add T4160RDB board support

T4160RDB shares the same platform as T4240RDB. T4160 is
a low power version of T4240, with the eight e6500 cores,
two DDR3 controllers, and same peripheral bus interfaces.

Signed-off-by: Chunhe Lan <Chunhe.Lan@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>