Where CACHED_TO_HYS() is still needed for kernel-virtual-to-physical
or physical-to-uncached mapping (fb drivers), replace with
`#include <mips/cpuregs.h>'.
based on "#ifdef MELLON": examine the framebuffer dimensions in the
fb softc, and initialize the x-axis offset appropriately.
User-level changes to (e.g.) an Xserver are still needed to work
on an SFB.
