drm/i915/vga: Convert VGA code to intel_display

drm/i915/vga: Convert VGA code to intel_display

struct intel_display will replace struct drm_i915_private as
the main thing for display code. Convert the VGA code to
use it (as much as possible at this stage).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240906143306.15937-5-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>