Mark CTL frontend's CAM driver as CAM_PERIPH_DRV_EARLY.

Target mode operation does not depend on the initiator mode scan process.
This change allows the target driver to attach earlier and receive some
async events (like AC_CONTRACT) that could be lost otherwise.

MFC after:	1 week

(cherry picked from commit 65ae10fa381c6147e1901d86d2e81478f5c52ca5)
Update isp_tgt_map and send new arrival notification if target that departed
earlier has returned.  Previously that code worked only once, confusing CTL.

MFC after:	1 month

(cherry picked from commit 8a81e148a45a5c56bc522c3a3b804839a9fa6cc3)