ARM: shmobile: defconfig: Enable CMA for DMA

To be able to use VIN with larger frame sizes CMA memory are needed for
DMA. If this is not enabled trying to capture large frames can result in
errors such as:

rcar-vin e6ef0000.video: dma_alloc_coherent of size 8388608 failed

A CMA area of 64MB are needed for v4l2-compliance to pass on all formats
on the largest possible frame size of 2048x2048.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>