hos: refactor fss to pkg3

To `fss0` config is now renamed to `pkg3`.
`fss0` still works but is deprecated.
Additionally `fss0experimental` key is now renamed to `pkg3ex`

Makefile

@@ -48,7 +48,7 @@ OBJS += $(addprefix $(BUILDDIR)/$(TARGET)/, \
 
 # Horizon.
 OBJS += $(addprefix $(BUILDDIR)/$(TARGET)/, \
-	hos.o hos_config.o pkg1.o pkg2.o pkg2_ini_kippatch.o fss.o secmon_exo.o \
+	hos.o hos_config.o pkg1.o pkg2.o pkg3.o pkg2_ini_kippatch.o secmon_exo.o \
 )
 
 # Libraries.