mtd: pxa32xx_nand: add support for partition table parsing

The pxa32xx_nand driver doesn't support partition tables from the
command line. This patch adds support for it.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>