a: re-work GPIO keys

Allow different levels to indicate press.
Remove DIP switches

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
a: set proper polarity for DIP switches (normally off)

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Merge branch 'staging' of github.com:boundarydevices/u-boot-imx6 into staging