drm/i915: Parse and set stepping for platforms with GMD

Expand the current stepping convention to accommodate the GMD
stepping info. Typically GMD step maps to letter stepping
by "A + step %4" and number to "A + step /4" i.e, GMD step
0 maps to STEP_A0, 1 to _A1, 2 to _A2, 3 to _A3, 4 to STEP_B0...

Future platforms might break this formulae and may require a table
mapping to decode GMD step compatible with the convention.

v2:
 - Pass the updated ip version structure
v3:
 - Skip using GMD to step table(MattR)

Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220916014648.1310346-3-radhakrishna.sripada@intel.com