drm/i915/fbc: Convert to intel_display, mostly

drm/i915/fbc: Convert to intel_display, mostly

Switch the FBC code over to intel_display from i915, as
much as possible. This is the future direction so that
the display code can be shared between i915 and xe more
cleanly.

Some of the platform checks and the stolen mem facing stiff
still need i915 around though.

v2: Drop some redundant to_i915() casts

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240705145254.3355-3-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>