find7s: Add support for find7s notification lights

PS4: Major rework
Based on CM/Gummy's find7s support, but with a lot of rework/fixes

Gummy/CM limits onMS/offMS to 500 - despite the fact that this
is the second shortest possible value
Change-Id: I9d3a2a7ee59c706ab793fe1ca0ea6f5e9d14949c