lxfb: extend PLL table to support dotclocks below 25 MHz

Extends the PLL frequency table of the AMD Geode-LX frame buffer driver to
make use of the DIV4 bit, thus adding support for dotclocks between 6 and 25
MHz.  These are needed for small LCDs (e.g.  320x240).  Also inserts some
intermediate steps between pre-existing frequencies.

Signed-off-by: Jens Rottmann <JRottmann@LiPPERT-AT.de>
Cc: Jordan Crouse <jordan.crouse@amd.com>
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>