ppc: xilinx-ppc440-generic: Cleanout header files

ppc: xilinx-ppc440-generic: Cleanout header files

Now that there is only one header file for all ppc440 files, merge
header files.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>