dmaengine: omap-dma: Dynamically allocate memory for lch_map

On OMAP1 platforms we do not have 32 channels available. Allocate the
lch_map based on the available channels. This way we are not going to have
more visible channels then it is available on the platform.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>