scripts: extract_dts_includes: Fix DeprecationWarning
scripts: extract_dts_includes: Fix DeprecationWarning

With python3.7 we get the following warning:

	extract_dts_includes.py:496: DeprecationWarning: Using or
	importing the ABCs from 'collections' instead of from
	'collections.abc' is deprecated, and in 3.8 it will stop
	working.

Fix this by using 'from collections.abc import Mapping' instead of
'import collections'.

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

nashif/zephyr,punitvara/zephyr,explora26/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,Vudentz/zephyr,ldts/zephyr,finikorg/zephyr,galak/zephyr,punitvara/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,punitvara/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,ldts/zephyr,ldts/zephyr,finikorg/zephyr,explora26/zephyr,Vudentz/zephyr,punitvara/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,nashif/zephyr,nashif/zephyr,ldts/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr