init: Add inotify for /dev/input/

Since event sources can come and go asynchronously because of delayed
driver instantiation due to initialization or firmware upload, USB
attched devices, kernel module loads, or test automation sources like
monkey, add in inotify on /dev/input/ to support these possibilities.

Test: manual, boot, check registered chord works
Bug: 64114943
Change-Id: Ie598bb6f5bf94b2034ab33cf3be7fa15d3467141