Switch SKL to use a revid->stepping table as we're trying to do on all
platforms going forward.  Also drop the preproduction revisions and add
the newer steppings we hadn't already handled.

Note that SKL has a case where a newer revision ID corresponds to an
older GT/disp stepping (0x9 -> STEP_J0, 0xA -> STEP_I1).  Also, the lack
of a revision ID 0x8 in the table is intentional and not an oversight.
We'll re-write the KBL-specific comment to make it clear that these kind
of quirks are expected.

v2:
 - Since GT and display steppings are always identical on SKL use a
   macro to set both values at once in a more readable manner.  (Anusha)
 - Drop preproduction steppings.

Bspec: 13626
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210713193635.3390052-4-matthew.d.roper@intel.com