ARM: bcm2835_defconfig: Increase CMA for VC4

The VC4 needs more memory than the default setting:

    cma: cma_alloc: alloc failed, req-size: 4096 pages, ret: -12
    vc4-drm soc:gpu: failed to allocate buffer with size 16777216

So increase the value to 32 MB and fix this issue.
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>

arch/arm/configs/bcm2835_defconfig

@@ -55,6 +55,7 @@ CONFIG_DEVTMPFS=y
 CONFIG_DEVTMPFS_MOUNT=y
 # CONFIG_STANDALONE is not set
 CONFIG_DMA_CMA=y
+CONFIG_CMA_SIZE_MBYTES=32
 CONFIG_SCSI=y
 CONFIG_BLK_DEV_SD=y
 CONFIG_SCSI_CONSTANTS=y