drm/i915: Implement IS_* macros using static tables

Instead of using the IS_I9XX etc macros that expand to a ton of
comparisons, use new struct intel_device_info to capture the
capabilities of the different chipsets.  The drm_i915_private struct
will be initialized to point to the device info that correspond to
the actual device and this way, testing for a specific capability is
just a matter of checking a bit field.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Signed-off-by: Eric Anholt <eric@anholt.net>