dmaengine: zynqmp_dma: fix burst length configuration

Since the dma engine expects the burst length register content as
power of 2 value, the burst length needs to be converted first.
Additionally add a burst length range check to avoid corrupting unrelated
register bits.

Signed-off-by: Matthias Fend <matthias.fend@wolfvision.net>
Link: https://lore.kernel.org/r/20200115102249.24398-1-matthias.fend@wolfvision.net


Signed-off-by: Vinod Koul <vkoul@kernel.org>