gma500: SDVO DDC bus guessing isn't working so hardcode it instead

We currently don't have support for parsing SDVO mappings from BIOS so we're
guessing the bus switch parameter. This isn't working so hardcode it to a
configuration known to work on most poulsbo hardware.

Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>