drm/i915/uncore: fwtable read handlers are now used on all forcewake platforms

With the recent refactor of the uncore mmio handling, all
forcewake-based platforms (i.e., graphics version 6 and beyond) now use
the 'fwtable' read handlers.  Let's pull the assignment out of the
per-platform if/else ladder to make this more obvious.

Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Suggested-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210923003029.2194375-1-matthew.d.roper@intel.com