arm/dt: msm8974: Disable Q6 MSS PIL device node for RUMI

The Q6 MSS PIL driver is not compatible with RUMI.  Linux
crashes if this driver is probed on a RUMI device.  Therefore,
configure the Q6 MSS PIL device node so that it is disabled for
RUMI.

Change-Id: Icf7284a7d13774a8b72deb31c178217c20c737a8
Signed-off-by: David Collins <collinsd@codeaurora.org>