drm/i915: Add release id version

Besides the arch version returned by GRAPHICS_VER(), new platforms
contain a "release id" to make clear the difference from one platform to
another.

The release id number is not formally defined by hardware until future
platforms that will expose it via a new GMD_ID register.  For the
platforms we support before that register becomes available we will set
the values in software and we can set them as we please. So the plan is
to set them so we can group different features under a single
GRAPHICS_VER_FULL() check.

After GMD_ID is used, the usefulness of a "full version check" will be
greatly reduced and will be mostly used for deciding workarounds and a
few code paths. So it makes sense to keep it as a separate field from
graphics_ver. Also, as a platform with `release == n` may be closer
feature-wise to `n - 2` than to `n - 1`, use the word "release" rather
than the more common "minor" for this

This is a mix of 2 independent changes: one by me and the other by Matt
Roper.

v2:
  - Reword commit message to make it clearer why we don't call it
    "minor" (Matt Roper and Tvrtko)
  - Rename variables s/*_ver_release/*_rel/ and print them in a single
    line formatted as {ver}.{rel:2} (Jani and Matt Roper)

Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210707235921.2416911-2-lucas.demarchi@intel.com