drm/i915/fbc: Moved fence related code away from intel_fbc

As a preparation for Xe move HW fence details away from intel_fbc code.
Add new functions to check support for legacy fencing and fence id and use
these in fbc code. Xe doesn't support legacy fencing.

v2: Fix intel_gt_support_legacy_fencing macro

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230614051731.745821-4-jouni.hogander@intel.com