mtd: maps: bcm963xx-flash: make CFE partition parsing an mtd parser

Recent BCM63XX devices support a variety of flash types (parallel, SPI,
NAND) and share the partition layout. To prevent code duplication make
the CFE partition parsing code a stand alone mtd parser to allow SPI or
NAND flash drivers to use it.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>