powerpc: Add P3041DS/P5020DS board support (uses corenet_ds code)

The P3041DS & P5020DS boards are almost identical (except for the
processor in them).  Additionally they are based on the P4080DS board
design so we use the some board code for all 3 boards.

Some ngPIXIS (FPGA) registers where reserved on P4080DS and now have
meaning on P3041DS/P5020DS.  We utilize some of these for SERDES clock
configuration.

Additionally, the P3041DS/P5020DS support NAND.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Shaohui Xie <b21989@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>