Increase priority for broadcast intent triggered by HW key

Add the FLAG_RECEIVER_FOREGROUND flag to the broadcast intent
triggered by hardware key.
This prevents the framework from delaying the delivery of the
intent to its recipients, and improves the response for hardware
key event under heavy load on the system.

Bug: 28735973
Change-Id: Ib7f219845be34794f4c7545927e53cc6c2b504a3