s: add NANDF_D7 (GP2:7) as GPIO power key

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
s: implement poweroff by pulling GP2:7 low

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Merge branch 'boundary-imx_3.0.35_4.0.0' of https://github.com/boundarydevices/linux-imx6 into boundary-imx_3.0.35_4.0.0