viafb: viafb.modes, viafb.txt

Correct via_fb_ to viafb_ and remove the Kconfig part in viafb.txt.

viafb.modes: supported mode table
viafb.txt: documentation of viafb driver

Signed-off-by: Joseph Chan <josephchan@via.com.tw>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>