target: init: Add runtime check is SSD feature enabled

Add runtime check function for SSD_ENABLE feature defined to
avoid ifdef-ery and improve readability of the code.

Change-Id: I239e00f30ff70b87eddfd7e09bd674cd01614587
diff --git a/include/target.h b/include/target.h
index b70306d..dc86864 100644
--- a/include/target.h
+++ b/include/target.h
@@ -47,6 +47,7 @@
 void target_serialno(unsigned char *buf);
 void target_fastboot_init(void);
 void target_load_ssd_keystore(void);
+bool target_is_ssd_enabled(void);
 struct mmc_device *target_mmc_device();