gma500: Add Poulsbo support

This provides the specific code for Poulsbo, some of which is also used for
the later chipsets. We support the GTT, the 2D engine (for console), and
the display setup/management. We do not support 3D or the video overlays.

In theory enough public info is available to do the video overlay work
but that represents a large task.

Framebuffer X will run nicely with this but do *NOT* use the VESA X
server at the same time as KMS. With a Dell mini 10 things like Xfce4 are
nice and usable even when compositing as the CPU has a good path to the
memory.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>