tgafb: TURBOchannel support

This is support for the TC variations of the TGA boards (properly known as
SFB+ or Smart Frame Buffer Plus boards).  The 8-plane SFB+ board uses the
Bt459 RAMDAC (unlike its PCI TGA counterpart, which uses the Bt485), so
bits have been added to support this chip as well.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: James Simmons <jsimmons@infradead.org>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>