[MTD] [NAND] remove dead Kconfig associated with !CONFIG_PPC_MERGE

Removed the Kconfig associated with 'NDFC NanD Flash Controller'.
We can't enable !CONFIG_PPC_MERGE so there is no way to enable
this.  Additionally the code needs to get updated for arch/powerpc.

For the time being lets just remove the Kconfig option so we can
actually remove CONFIG_PPC_MERGE.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>