mtd: nand: pxa3xx: Add bad block handling

Add support for flash-based bad block table using Marvell's
custom in-flash bad block table layout. The support is enabled
a 'flash_bbt' platform data or device tree parameter.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>