davinci-pcm uses 16 as the no.of periods. With this, in EDMA we have to
allocate atleast 17 slots: 1 slot for channel, and 16 slots the periods.
Due to this, the MAX_NR_SG limitation causes problems, set it to 20 to make
cyclic DMA work when davinci-pcm is converted to use DMA Engine. Also add
a comment clarifying this.
Signed-off-by: Joel Fernandes <joelf@ti.com> Signed-off-by: Vinod Koul <vinod.koul@intel.com>