greybus: connection: switch to using spin_lock_irqsave/spin_lock_irqrestore excluisvely

We know that it is a bad idea to explicitly enable IRQs when we don't
don't know if they were already off before we disabled, so switch to the
save _irqsave and _irqrestore functions.

Ultimately, we need to review places in the Greybus drivers where IRQs
are disabled and remove unnecessary instances. This is only an interim
step.

This code will never run from hard irq context, as it is already taking
mutex in the path.

Testing done: booted EVT2.0, ran suspend/resume test app with a period
of 20s for a few dozen cycles.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Jeffrey Carlyle <jcarlyle@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>