flashy-eaa1917

javaisland: add flashy support

Summary: Add the flashy support for JavaIsland platform.

Test Plan: Built flash with tools/flashy/build.sh

Reviewed By: williamspatrick

Differential Revision: D55333620

fbshipit-source-id: 86363e06b8d98f020f0ebe25a91e0950c5cb164b