Change is_idle functions so it would be more usable outside debugfs.

Do this by replacing seq_file parameter with regular string.
Signed-off-by: Dani Liberman <dliberman@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>