MFC r352363:

Apply a runtime patch to the FDT data for imx6 to fix iomuxc problems.

The latest imported FDT data defines a node for an iomuxc-gpr device,
which we don't support (or need, right now) in addition to the usual
iomuxc device. Unfortunately, the dts improperly assigns overlapping
ranges of mmio space to both devices. The -gpr device is also a syscon
and simple_mfd device.

At runtime the simple_mfd driver attaches for the iomuxc-gpr node, then
when the real iomuxc driver comes along later, it fails to attach because
it tries to allocate its register space, and it's already partially in
use by the bogus instance of simple_mfd.

This change works around the problem by simply disabling the node for
the iomuxc-gpr device, since we don't need it for anything.

Approved by: re@ (gjb)