drm/i915: remove indirection in the PCI ID macros

Spell all the PCI IDs out to be able to quickly grep for the IDs. No
functional changes.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
[danvet: Add GT1/2 to comments to not loose that distinction.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>