video: Fix the HGA framebuffer driver

Resurrected some old hardware and fixed up the hgafb driver to work
again. Only tested with fbcon, since most fbdev-based software appears
to only support 12bpp and up. It does not appear that this driver has
worked for at least the entire 2.6.x series, perhaps since 2002.

Hercules graphics hardware uses packed pixels horizontally, but rows are
not linear. In other words, the pixels are not packed vertically. This
means that custom imageblit, fillrect and copyarea need to be written
specific to the hardware.

 * Removed the experimental acceleration option, since it is required
   for the hardware to work.
 * Fixed imageblit to work with fb_image's wider than 8 pixels.
 * Updated configuration text (HGA hardware is from 1984)

Signed-off-by: Brent Cook <busterb@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>