(address error faults), as well as other reported problems:
- Simplify grfmv_phys() to work like grfiv_phys(), and eliminate the
second argument to both, as we don't use it anyway.
- Handle fbbase and fboff consistently throughout. Closes PR 3862.
- Eliminate grfaddr() by pulling it into grfmmap(), which is the
only place it was used, previously.
- grfmap() now gets the physical address of the framebuffer from
the appropriate driver, rather than try to compute it by itself.
Be careful with aligning the base to a page address and increase
the length of the mapped region appropriately. Closes PR 2867.