dpll: extend lock_status_get() op by status error and expose to user

Pass additional argunent status_error over lock_status_get()
so drivers can fill it up. In case they do, expose the value over
previously introduced attribute to user. Do it only in case the
current lock_status is either "unlocked" or "holdover".

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>