ARM: mxc: Remove setting of consistent dma size

All in-tree MX boards using video use memblock_* functions to get their
coherent dma space for the camera. So there is no need to increase
CONSISTENT_DMA_SIZE beyond the default 2MB and we can simply remove the
defines which do this.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>