target: init: Add weak function for SSD keystore loading

The SSD feature is used to protect proprietary images. Loading of
keystrore should be implemented per target (if needed) and it will
be called in aboot init just before linux entry point.

Change-Id: Id45b20135c29e972a5e84942e558b623644de661
diff --git a/target/init.c b/target/init.c
index 8a9a9d0..3b2f432 100644
--- a/target/init.c
+++ b/target/init.c
@@ -107,6 +107,9 @@
 #endif
 }
 
+__WEAK void target_load_ssd_keystore(void)
+{
+}
 
 /* Default target does not support continuous splash screen feature. */
 __WEAK int target_cont_splash_screen()