I'm reviving an old patch from 2009 that adds support for GXT4000P and GXT6500P
adapter to the gxt4500 driver.

See threads at http://marc.info/?l=linux-fbdev-devel&m=124345080216952&w=2
and https://lists.ozlabs.org/pipermail/linuxppc-dev/2009-June/072672.html
for more details.

This patch adds support for GXT4000P and GXT6500P cards found on some
IBM pSeries machines.
GXT4000P/6000P and GXT4500P/6500P  couples are  identical from
software's point of view and are based on the same  Raster Engine
(RC1000), except for a different reference clock for the PLL.
GXT6x00P models are equipped with an additional Geometry Engine
(GT1000) but this driver doesn't use it.
Signed-off-by: Nico Macrionitis <acrux@cruxppc.org>
Signed-off-by: Giuseppe Coviello <cjg@cruxppc.org>
Tested-by: Dan Horák <dan@danny.cz>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>