dts: Fix warning related to arm,v{6,7,8}m-nvic yaml files

The nvic yaml files were missing an id property.  So we'd get a warning
like:

extract_dts_includes.py: 'id' property missing in 'ARMv7-M NVIC Interrupt Controller' binding. Using '<unknown id>

Add the id to fix this warning.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>