try to make VIC-II logical raster numbers match C64.
physical rasters translate to VIC-II logical rasters using a
piece-wise linear approximation.
set options for configuring from flash at maximum speed.
(66Mhz, quad speed transfer, should give 52MB/sec.
 4MB config should thus load in <100ms).
plumb in serial configuration flash so that we can programme it
from booted machine.
fix various multi-colour text/bitmap mode bugs.
disable QspiSCK pin, since ISE doesn't seem to be able to target it.
fix typo in corrections to monocolour mode.