SGDMA write_waitrequest always 'high'

Only worry about waitrequest getting stuck high if the master is issuing a read or write (otherwise the master ignores it). I also recommend getting the SGDMA working using polling code first and then when that's working then switch over to using interrupts.

In order to get the SGDMA started you need the following (at a minimum):

1) At least two descriptors allocated

2) Make sure the descriptor at the end of the chain has the owned by hardware bit set low

3) Write the pointer of the first descriptor to the SGDMA CSR slave port

4) Write to the go bit of the SGDMA CSR slave port

After# 4 you should see the SGDMA ready signal assert high, data becomes accepted, and eventually the write master will being writing out the data.