gnss: sirf: fix premature wakeup interrupt enable

Make sure the receiver is powered (and booted) before enabling the
wakeup interrupt to avoid spurious interrupts due to a floating input.

Similarly, disable the interrupt before powering off on probe errors and
on unbind.

Fixes: d2efbbd1 ("gnss: add driver for sirfstar-based receivers")
Cc: stable <stable@vger.kernel.org>	# 4.19
Signed-off-by: Johan Hovold <johan@kernel.org>