powerpc/44x: Warp patches for the new NDFC driver

Convert the Warp platform to use the newly merged NDFC driver

- warp.dts changed to work with ndfc
- warp-nand.c no longer needed
- removed obsolete rev A support from cuboot-warp.c

Signed-off-by: Sean MacLennan <smaclennan@pikatech.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>