"kvstore_global_api" requires "kvstore" for backward compatibility

PR ARMmbed#13908 replaces the umbrella library for all KVStore from
"kvstore_global_api" to "kvstore". Now "kvstore_global_api"
still exists but is restricted to the global API part only.

By adding "kvstore" as a dependency of "kvstore_global_api",
existing bare metal projects (e.g. mbed-bootloader) that use
the latter library name to pull in the KVStore prototype class
will continue to work.

Author: LDong-Arm

storage/kvstore/kvstore_global_api/mbed_lib.json

@@ -1,3 +1,4 @@
 {
-    "name": "kv-global-api"
+    "name": "kv-global-api",
+    "requires": ["kvstore"]
 }