s3fb: limit 8x16 rectangles when tileblitting is enabled

If tileblitting is enabled (text mode), the hardware can only accept 8x16
bitmaps. Advertise this to the upper layer. And to ensure that an appropriate
font is always available, select an 8x16 font in Kconfig.

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>