add AGP configuration registers for i840/855PM, i840/i850E, 82443LX/BX/GX
Although there chips are well alike, but initialization and so on procedures differ.
FreeBSD, with cleanup/KNF by me.
Note: These chipsets are not well supported by the i810 driver in
NetBSD's in-tree xsrc (based on XFree86 4.2.1 at this time). However,
the driver works perfectly using bleeding-edge XFree86-current on my
Omnibook's i830MG with these agp changes.
perry