msm: display: support for no DMA pipes

The dt_parser currently expects some value for the number of DMA
pipes. mpq8092 doesn't have dma pipes.

Change-Id: I8152de21df609448f76b7ded141f532e38553832
Signed-off-by: Zohaib Alam <zalam@codeaurora.org>
Signed-off-by: Ken Zhang <kenz@codeaurora.org>