We're using imx_v6_v7_defconfig on our Wandboards. After upgrading to v4.14.67, reboot no longer works (or, well, takes a very long time when the watchdog is configured).
v4.14.66 works fine, the breakage bisects to 2059e527a659cf16d6bb709f1c8509f7a7623fc4 (ARM: imx_v6_v7_defconfig: Select ULPI support), and reverting that on top of v4.14.67 again works.
Rasmus