mtd: nand: Allow to build pxa3xx_nand on Orion platforms

The Armada 370 and Armada XP SoC families, selected by PLAT_ORION,
have a Nand Flash Controller (NFC) IP very similar to the one present
in PXA platforms. Therefore, we want to build this driver on PLAT_ORION.

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>