msm: modem_notifier: export modem_notifier initialization function

Export msm_init_modem_notifier_list() so that it may be called from within
a board file inorder to satisfy driver probe order dependencies.

Change-Id: I6671bb6ab9419e5f1da9cf4a714dcf53844a6d0e
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>