this happens on 11.0-RELEASE and 11.1-BETA2. Even more annoying is that Xorg xf86-video-intel driver loads both kernel modules and causes the same panic (since March this year). I reduced it to a simple sequence of kldload commands.
Steps to reproduce (on many systems one of the modules is already loaded in /boot/loader.conf):
1) kldload i915kms
2) kldload i915
Both modules want to install the device /dev/dri/card0 which causes a clash (errno EEXIST) and a subsequent panic.
panic: make_dev_sv: bad si_name (error=17, si_name=dri/card0)
Only one of the kernel modules should load. The other subsequent kldload should fail to load without causing a panic.