mtd: bcm63xxpart: add of_match_table support

Add of_match_table support to allow using bcm63xxpart as a full flash
layout parser from device tree.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>