T4160 is a subset of T4240. Merge them in config_mpc85xx.h to simplify
the defines. Also move CONFIG_E6500 out of t4qds.h into config_mpc85xx.h.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>