kms/cursor-manager: Create CrtcStateImpls for all active CRTCs
even if they don't have a cursor plane. This way we can just use the object. Updating the cursor plane then just looks at the cursor_plane field to skips updates when there is none.
Closes: #3254 (closed) Fixes: cc7bca07 ("crtc/kms: Dynamically assign primary and cursor planes")