fb/intelfb: conflict with DRM_I915 and hide by default

Users get confused by this driver.  It's really a special purpose
embedded driver, and causes a lot of problems if enabled.  So hide it
under EMBEDDED by default, and make sure it doesn't get enabled with
the i915 DRM driver.

Dave, I'm hoping you can feed this to Linus through your tree.  It's
appropriate for 2.6.31 I think.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>