drivers: dma-coherent: add initialization from device tree

Initialization procedure of dma coherent pool has been split into two
parts, so memory pool can now be initialized without assigning to
particular struct device.  Then initialized region can be assigned to more
than one struct device.  To protect from concurent allocations from
structure.  The last part of this patch adds support for handling
'shared-dma-pool' reserved-memory device tree nodes.

[akpm@linux-foundation.org: use more appropriate printk facility levels]
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Josh Cartwright <joshc@codeaurora.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>