MTD: NAND: JZ4740: Multi-bank support with autodetection

The platform data can now specify which external memory banks to probe
for NAND chips, and in which order. Banks that contain a NAND are used
and the other banks are freed.

Squashed version of development done in jz-2.6.38 branch.
Original patch by Lars-Peter Clausen with some bug fixes from me.
Thanks to Paul Cercueil for the initial autodetection patch.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3560/
Acked-By: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>