drm/i915/display: allow to skip certain power wells

This allows us to skip power wells on a platform allowing it to re-use
the table from another one instead of having to create a new table from
scratch that is basically a copy with a few removals.

Cc: Imre Deak <imre.deak@intel.com>
Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Aditya Swarup <aditya.swarup@intel.com>
[ Adapt ignore logic to be based on pw id rather than adding a new
  field, as suggested by Imre ]
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/20201014191937.1266226-1-lucas.demarchi@intel.com