ARM: dts: imx6-logicpd: Re-enable SNVS power key

The baseboard of the Logic PD i.MX6 development kit has a power
button routed which can both power down and power up the board.
It can also wake the board from sleep.  This functionality was
marked as disabled by default in imx6qdl.dtsi, so it needs to
be explicitly enabled for each board.

This patch enables the snvs power key again.

Signed-off-by: Adam Ford <aford173@gmail.com>
Fixes: 770856f0 ("ARM: dts: imx6qdl: Enable SNVS power key according to board design")
Cc: stable <stable@vger.kernel.org> #5.3+
Signed-off-by: Shawn Guo <shawnguo@kernel.org>