intel: add generic functions to check PCI ID

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>