trusty: move probe to subsys_initcall

Child devices of trusty like FIQ-based debuggers and watchdogs may
want to probe early, move trusty from module init to subsys init
to allow it and its children to probe earlier.

Change-Id: I10d7028d5c7dbeb4dc5e951029c059783b1953d3
Signed-off-by: Colin Cross <ccross@android.com>