Update PreBootBroadcaster to use ProcessRecord.

In order to receive valid "resultTo" responses, we now need to know
the ProcessRecord to deliver them through, which in this case is the
"system_server" process.

Bug: 251486235
Test: manual
Change-Id: Iaf1b2e5d6a1da5bc59e297d82d941c6d4cfe7ab3