drivers: of: Export of_reserved_mem_device_{init,release}

Export of_reserved_mem_device_{init,release} so that modules
can initialize and release their assigned per-device cma_area.

Signed-off-by: George G. Davis <george_davis@mentor.com>
[robh: s/EXPORT_SYMBOL/EXPORT_SYMBOL_GPL/]
Signed-off-by: Rob Herring <robh@kernel.org>