drm/xe/lnl: Drop pre-production workaround support

drm/xe/lnl: Drop pre-production workaround support

LNL has been out long enough that all of our internal usage of
pre-production hardware has been phased out and we no longer need to
maintain workarounds that were exclusive to pre-production parts.

Production LNL hardware always has B0 or later steppings for both
graphics and media IP.  Eliminate all workarounds that were exclusive to
A-step hardware and set the 'has_prod_wa_only' device flag for LNL to
make sure we warn and taint if someone tries to load the driver on an
old pre-production part.

Bspec: 70821
Reviewed-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Link: https://patch.msgid.link/20251212181411.294854-4-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>