util_dac_unpack: Make number of channels and channel width configurable

Always using 128bit for the input word unnecessarily increases the DMA
alignment requirements. This breaks existing software which assumes that the
DMA alignment requirement is 64bit.

So make it configurable whether we want 8 or 4 channels and while we are at
it also make the channel width configurable.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
fmcomms2: c5soc: Connect ADC, DAC and VGA DMA to different bridge interconnects

We have enough bridge interconnect to give each DMA its own, so use them.
This makes sure that they do not interfere with each others transfers to
much. The SDRAM controller side of the FPGA2SDRAM bridges FIFO runs at a
much faster frequency then what we are able to use in the fabric. So its
better to do the arbitration on that side of the bus to make sure that we
can utilize the buses in the FPGA fabric to the maximum for each DMA core.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
fmcomms2: c5soc: Set dac_util_unpack number of channels to 4

We only do have 4 channels in this design. Reducing the number of supported
channels for the dac_util_unpack core to 4 from 8 lowers the DMA alignment
requirement from 128bit to 64bit.  We need this since applications only
expect a DMA alignment requirement of 64bit.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>