drivers: dma-contiguous: clean source code and prepare for device tree

This patch cleans the initialization of dma contiguous framework. The
all-in-one dma_declare_contiguous() function is now separated into
dma_contiguous_reserve_area() which only steals the the memory from
memblock allocator and dma_contiguous_add_device() function, which
assigns given device to the specified reserved memory area. This improves
the flexibility in defining contiguous memory areas and assigning device
to them, because now it is possible to assign more than one device to
the given contiguous memory area. Such split in initialization procedure
is also required for upcoming device tree support.

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>
diff --git a/include/linux/device.h b/include/linux/device.h
index bcf8c0d..9200cfd 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -711,7 +711,7 @@
 
 	struct dma_coherent_mem	*dma_mem; /* internal for coherent mem
 					     override */
-#ifdef CONFIG_CMA
+#ifdef CONFIG_DMA_CMA
 	struct cma *cma_area;		/* contiguous memory area for dma
 					   allocations */
 #endif