kbuild: remove src and obj from the top Makefile

Replace $(src) and $(obj) with $(srctree) and $(objtree), respectively.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/Makefile b/Makefile
index 66a3bcb..99336b6 100644
--- a/Makefile
+++ b/Makefile
@@ -248,9 +248,6 @@
 export KBUILD_CHECKSRC KBUILD_EXTMOD KBUILD_SRC
 
 objtree		:= .
-src		:= $(srctree)
-obj		:= $(objtree)
-
 VPATH		:= $(srctree)
 
 export srctree objtree VPATH
@@ -1717,7 +1714,7 @@
 endif
 checkstack:
 	$(OBJDUMP) -d vmlinux $$(find . -name '*.ko') | \
-	$(PERL) $(src)/scripts/checkstack.pl $(CHECKSTACK_ARCH)
+	$(PERL) $(srctree)/scripts/checkstack.pl $(CHECKSTACK_ARCH)
 
 kernelrelease:
 	@echo "$(KERNELVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"
@@ -1736,11 +1733,11 @@
 
 tools/: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(src)/tools/
+	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
 
 tools/%: FORCE
 	$(Q)mkdir -p $(objtree)/tools
-	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(src)/tools/ $*
+	$(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(tools_silent) $(filter --j% -j,$(MAKEFLAGS))" O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ $*
 
 # Single targets
 # ---------------------------------------------------------------------------