drm/i915: finish INTEL_GEN and friends conversion

Commit 161058fb ("drm/i915: Add remaining conversions to GRAPHICS_VER")
did the last conversions to the new macros for version checks, but left
one instance behind and some other changes sneaked in to use INTEL_GEN.
Remove the last users so we can remove the macros.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210707181325.2130821-3-lucas.demarchi@intel.com