Some AUTO updates
Testbench for testing VGA controller in isolation.
Fix a bug where the bus could lock up.
axi_arready would be asserted in STATE_ARBITRATE, in many cases to the wrong master.  That master would then wait forever for the transaction to complete.  The fix is to only assert the arready signals in STATE_ISSUE_ADDRESS.
Modify VGA controller to be more tolerant of underruns.  It now waits until the beginning of the next frame to begin refilling the pixel FIFO, and removes any entries from the FIFO at that point.