Dma transfer fixes

This MR fixes problem with data transfers I encountered during piezo capacitance measurement. It occurred that the data that are trasfered must be aligned with page size (4KB) and the piezo does not like changing its buffer size - now its size is fixed to 16 KB.

It is also needed to change the h2c_timeout on the xdma driver side. Currently it's 10 seconds. It's definitely too much. But I don't know where it should be reported.