intel: get gen once for gen >= 9

We don't need to call IS_GEN() for each gen >= 9: we can rather use the
new intel_is_genx() helper to iterate the pciids array once.

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>