Send USER_UNLOCKED broadcasts before PRE_BOOT.

Apps handling the PRE_BOOT_COMPLETED broadcast expect the user to be
fully unlocked and working.  Most system internals are using the
SystemServer interface, and we dispatch the unlocked event through
them before starting the PRE_BOOT process.

However, there are still some system internals that haven't been
converted to SystemServer, so we need to also send USER_UNLOCKED
for them to pick up before starting PRE_BOOT work.

Bug: 28086245
Change-Id: Ie847b463ea55a6dddcc49d243ef8fb308e5179a7