Implement support for parsing/interacting with NCAs. (#942)

* fs: implement support for interacting with ncas.

* spl: extend to use virtual keyslots

stratosphere/ams_mitm/source/amsmitm_main.cpp

@@ -81,7 +81,7 @@ void __appInit(void) {
         R_ABORT_UNLESS(fsInitialize());
         R_ABORT_UNLESS(pmdmntInitialize());
         R_ABORT_UNLESS(pminfoInitialize());
-        R_ABORT_UNLESS(splFsInitialize());
+        spl::InitializeForFs();
     });
 
     ams::CheckApiVersion();
@@ -89,7 +89,7 @@ void __appInit(void) {
 
 void __appExit(void) {
     /* Cleanup services. */
-    splFsExit();
+    spl::Finalize();
     pminfoExit();
     pmdmntExit();
     fsExit();