scripts: dts: gen_legacy_defines: mark DT_INST macros deprecated
scripts: dts: gen_legacy_defines: mark DT_INST macros deprecated

Add a __WARN("Macro is deprecated") to all DT_INST macros now that all
in tree users should have been converted to the new macros.

This is intended to make sure any PRs don't introduce new usages of
these macros.

Signed-off-by: Kumar Gala <a5e5248af4cd4f0ed8c515f61d40a6e2db46a66e@linaro.org>

zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr