libstagefright: Add custom IOCTL for prefetching CMA data for wv playback

trigger allocation of cma pool at start of drm playback

Change-Id: I6c15b31ff3147739f9d837a2a2b6e135cc918e99

libstagefright: Prefetch CMA data for secure playback via MediaCodec

Trigger allocation of cma pool at start of drm playback in mediacodec mode.

Change-Id: I1ce09f3c9013cb815f1ab0e729a099c7aae79ec5