doc: add --no-index-modules option to genrest.py
doc: add --no-index-modules option to genrest.py

This add a new option `--no-index-modules` which works similarly to
`--modules` but does not generated index pages, only retains the
tweaking of how paths are displayed on symbol information pages,
showing '<title>/path/within/module/Kconfig' for paths that fall
within modules.

This is required by NCS, where there are more "modules" which we don't
want to have indexes for.

Signed-off-by: Fabio Utzig <382671175562e0df8128054dbdb05a250d79f588@nordicsemi.no>

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