greybus: gpio: fix atomic sleep when using interrupts

The irq-chip callbacks are made in atomic context where we must not do
any synchronous greybus operations.

Fix the current gpio-interrupt implementation by using the bus-lock
functionality provided by the irq subsystem.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>