Dear NXP:
[ 18.684772] reboot: Restarting system
[ 18.688457] CPU: 0 PID: 440 Comm: reboot Not tainted 4.9.11-1.0.0+gc27010d99a3d #6
[ 18.696032] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 18.702597] [<8010f954>] (unwind_backtrace) from [<8010b398>] (show_stack+0x10/0x14)
[ 18.710359] [<8010b398>] (show_stack) from [<803c0918>] (dump_stack+0x78/0x8c)
[ 18.717597] [<803c0918>] (dump_stack) from [<80109ac0>] (machine_restart+0xc/0x80)
[ 18.725181] [<80109ac0>] (machine_restart) from [<8014c640>] (SyS_reboot+0xc8/0x1ac)
[ 18.732937] [<8014c640>] (SyS_reboot) from [<80107880>] (ret_fast_syscall+0x0/0x3c)
[ 18.840659] imx2-wdt 20c0000.wdog: failed to assert external reset, trying with timeout
[ 19.848669] Reboot failed -- System halted
If you don't have PMIC you can't use the external reset.
In this case keep wdog1 enabled and wdog2 disabled, which is the default configuration for imx6qdl.dtsi:
imx6qdl.dtsi\dts\boot\arm\arch - linux-imx - i.MX Linux kernel
This is overriden in SABRE SD EVK dts:
imx6qdl-sabresd.dtsi\dts\boot\arm\arch - linux-imx - i.MX Linux kernel
so you need to make sure wdog1 and wdog2 configuration from imx6qdl.dtsi is not overridden somewhere in your board dts hierarchy.