Clear 40-pin IO muxing on Dev Board

The iomuxc group for the 40-pin gpio takes ownership of GPIO that are
used by the enviro board. Set the phanbell_gpio property to owning no
GPIO and instead rely on the enviro one for the needed IOs.

Tested:
Operational ADC with overlay applied

Change-Id: I11b2446bf6829a80ce9366c2051f937953ed82ac
2 files changed