Camera: Add hotplug support (for fixed # of cameras)

* Minor: also change addListener to fire the current status upon subscription
* Minor: STATUS_AVAILABLE is now an alias for STATUS_PRESENT and deprecated

Change-Id: I254608a7332095e3ef201ffea64cff156cfc1b3e (reverted from commit a36381479c5c546a01188390f1e0d2e280a3dbd8)
Signed-off-by: ayysir <dresadd09691@gmail.com>