This will allow platforms to reuse kernel IDs instead of manually
keeping them in sync. In most of the cases we only need to extend
IS_9XX().  Current platforms that fit this requirement can be ported
over to use this macro. Right now it's a nop since it doesn't have any
PCI ID added.

The i915_pciids.h header is in sync with kernel tree on
drm-tip 2018y-08m-20d-21h-41m-11s.

v2: - move to a separate .c so we can have the array in a single
      compilation unit
    - use a single array for all gens
    - add real functions to get or check gen by pciid
    - define our own pci device struct rather than inherit the one
      kernel uses: we can throw away most of the fields

v3: - add comment to keep ids sorted by gen
    - remove misleading comment about all gens

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>