I am using some icons from Material Icons site by google. They provided the icon from mdpi to xxxhdpi. What about the ldpi devices?
In terms of devices in active use and using the Play Store, you can find out the breakdown of screen sizes and densities in the device dashboards, updated monthly. The December 2016 edition of the dashboards shows 1.5% of devices are ldpi devices.
If you do not ship ldpi artwork, Android will down-sample some other density (e.g., mdpi). You may wish to test your icons on ldpi hardware to see how your icons look, and ship your own ldpi replacement for those icons that do not down-sample well.