make: ftl: add separate Makefile

Makefile

@@ -36,11 +36,6 @@ obj-y += source/fs/mufs/path.o
 obj-y += source/fs/mufs/super.o
 obj-y += source/fs/mufs/tree.o
 
-obj-y += source/ftl/dev.o
-obj-y += source/ftl/ftl.o
-obj-y += source/ftl/gc.o
-obj-y += source/ftl/map.o
-
 obj = $(addprefix $(BUILD)/, $(obj-y))
 
 # Include the dependencies.

source/Makefile

@@ -1,2 +1,3 @@
+-include source/ftl/Makefile
 -include source/platform/Makefile
 -include source/shell/Makefile

source/ftl/Makefile

@@ -0,0 +1,4 @@
+obj-y += source/ftl/dev.o
+obj-y += source/ftl/ftl.o
+obj-y += source/ftl/gc.o
+obj-y += source/ftl/map.o