make: separate Makefile for shell commands

Makefile

@@ -41,16 +41,6 @@ obj-y += source/ftl/ftl.o
 obj-y += source/ftl/gc.o
 obj-y += source/ftl/map.o
 
-obj-y += source/shell/args.o
-obj-y += source/shell/boot.o
-obj-y += source/shell/cmd.o
-obj-y += source/shell/echo.o
-obj-y += source/shell/flash.o
-obj-y += source/shell/ftl.o
-obj-y += source/shell/mufs.o
-obj-y += source/shell/rtc.o
-obj-y += source/shell/version.o
-
 obj = $(addprefix $(BUILD)/, $(obj-y))
 
 # Include the dependencies.

source/Makefile

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

source/shell/Makefile

@@ -0,0 +1,9 @@
+obj-y += source/shell/args.o
+obj-y += source/shell/boot.o
+obj-y += source/shell/cmd.o
+obj-y += source/shell/echo.o
+obj-y += source/shell/flash.o
+obj-y += source/shell/ftl.o
+obj-y += source/shell/mufs.o
+obj-y += source/shell/rtc.o
+obj-y += source/shell/version.o