update modedb.txt documentation about mode_option parameter change

Add names of drivers converted to "mode_option" parameter.

This is one step toward changing all fb drivers to have common "mode_option"
parameter.
Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/fb/modedb.txt

@@ -125,8 +125,12 @@ There may be more modes.
     amifb	- Amiga chipset frame buffer
     aty128fb	- ATI Rage128 / Pro frame buffer
     atyfb	- ATI Mach64 frame buffer
+    pm2fb	- Permedia 2/2V frame buffer
+    pm3fb	- Permedia 3 frame buffer
+    sstfb	- Voodoo 1/2 (SST1) chipset frame buffer
     tdfxfb	- 3D Fx frame buffer
     tridentfb	- Trident (Cyber)blade chipset frame buffer
+    vt8623fb	- VIA 8623 frame buffer
 
 BTW, only a few drivers use this at the moment. Others are to follow
 (feel free to send patches).