mtd: plat_nand: Add default partition parser to driver

Use cmdlinepart as the default partition parser and allow the arch setup code
to still use their own partition parsers.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>