ARM: dts: imx6qdl-phytec: handle unneeded MFD-subdevices correctly

The proper way to handle partly used MFD devices are to describe all MFD
subdevices in the devicetree and disable the not used ones. This
suppresses any warnings that may arise as a result.

Signed-off-by: Yunus Bas <y.bas@phytec.de>
Signed-off-by: Andrej Picej <andrej.picej@norik.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>