Documentation: bindings: Update bindings for Neutrino

Update bindings for Neutrino by adding new power supply gpio
item and making some other items optional since they depend
on hardware design.

Change-Id: Id2ed51aa6fe7290f6af1ddab5fa5708585de9053
Signed-off-by: Gustavo Solaira <gustavos@codeaurora.org>
CRs-Fixed: 1049904