arm: dts: msm8929: Set low-is-dual in simslot node

 * The simslot count is reported wrongly on J7 devices by the simslot
   driver, so set low-is-dual so that the gpio reading logic of the sim
   count gpio is inverted, and simlot count is reported correctly.

Change-Id: I82d963ec8e6f59f329ee8843cc10890c6b7e956d