drm/i915: Make wa list per-gt

Support for multiple GT's within a single i915 device will be arriving
soon.  Since each GT may have its own fusing and require different
workarounds, we need to make the GT workaround functions and multicast
steering setup per-gt.

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@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/20210917170845.836358-1-matthew.d.roper@intel.com