drivers: of: add initialization code for dma reserved memory

This patch adds device tree support for contiguous and reserved memory
regions defined in device tree.

Large memory blocks can be reliably reserved only during early boot.
This must happen before the whole memory management subsystem is
initialized, because we need to ensure that the given contiguous blocks
are not yet allocated by kernel. Also it must happen before kernel
mappings for the whole low memory are created, to ensure that there will
be no mappings (for reserved blocks) or mapping with special properties
can be created (for CMA blocks). This all happens before device tree
structures are unflattened, so we need to get reserved memory layout
directly from fdt.

Later, those reserved memory regions are assigned to devices on each
device structure initialization.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Rob Herring <rob.herring@calxeda.com>