[MTD] [NAND] pxa3xx_nand: moved some helper variables out from platform data

This patch moves some attributes out from the platform data into the
dynamically created nand device.   This results into a cleaner interface
and allows to use constant pxa3xx_nand_flash definitions.

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