gma500: Move the basic driver out of staging

This driver supports unaccelerated KMS display, and accelerated console
handling on the Intel Poulsbo, Oaktrail, Cedarview and Medfield hardware.

For the initial merge Medfield will be left out as it needs considerable
further work to reach a decent standard

Begin by adding the Makefiles and Kconfig. These are not yet plumbed into
the DRM layer so will have no effect on their own

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