arm64: dts: imx8mp-tqma8mpql-mba8mpxl: Enable wakeup-source for GPIO buttons

These buttons are capable of waking up a suspended system, add the
appropriate property for both.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>