[MTD] [NAND] pxa3xx_nand: allow to define flash types in the platform data

This patch adds 'flash' and 'num_flash' attributes to the platform data.
There was added code in the driver to iterate across these attributes in the
detect-flash routine.  This is done similarly to the existing method
which uses a 'builtin_flash_types' field.

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>