defconfig: arm: msm: Configure common CMA size to 16MB

We need 16MB of default CMA region on msmtitanium.
So disable CONFIG_CMA_SIZE_MBYTES config which was
setting CMA region to 8MB. By default we
reserve 16MB for common CMA region if config is
not enabled.

Change-Id: Ia8b250b4f7c4fedfd9e3118e4e3c582af31bc5e3
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>