Input: snvs_pwrkey - send key events for i.MX6 S, DL and Q

The first generation i.MX6 processors does not send an interrupt when the
power key is pressed. It sends a power down request interrupt if the key is
released before a hard shutdown (5 second press). This should allow
software to bring down the SoC safely.

For this driver to work as a regular power key with the older SoCs, we need
to send a keypress AND release when we get the power down request irq.

Signed-off-by: Robin van der Gracht <robin@protonic.nl>
Link: https://lore.kernel.org/r/20191125161210.8275-1-robin@protonic.nl
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>