mtd: nand: pxa3xx: Handle ECC and DMA enable/disable properly

When ECC is not selected, the ECC enable bit must be cleared
in the NAND control register. Same applies to DMA.

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>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>