kernel: dma-contiguous: mark CMA parameters __initdata/__initconst

These parameters are only referenced by __init routine calls during
early boot so they should be marked as __initdata and __initconst
accordingly.

Signed-off-by: Shyam Saini <mayhs11saini@gmail.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>