metag: Use get_signal() signal_setup_done()

Use the more generic functions get_signal() signal_setup_done()
for signal delivery.

[James Hogan: avoid reordering get_signal() and restart check.]

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: James Hogan <james.hogan@imgtec.com>