init: Add init extension library for MSM8916

Without this one, LIBINIT_USE_MSM_DEFAULT is set true and init_msmdefault.c get built so that device-specific init file (defined via TARGET_LIBINIT_DEFINES_FILE) doesn't work!

Change-Id: Iced9daa1d723eac1c3b09b4f793e95d2cecc7bb4