tools: convert makefiles to kbuild style

Before this commit, makefiles under tools/ directory
were implemented with their own way.

This commit refactors them by using "hostprogs-y" variable.

Several C sources have been added to wrap other C sources
to simplify Makefile.
For example, tools/crc32.c includes lib/crc32.c

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/tools/env/Makefile b/tools/env/Makefile
index 27892f7..c303815 100644
--- a/tools/env/Makefile
+++ b/tools/env/Makefile
@@ -5,15 +5,8 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-HOSTSRCS := $(SRCTREE)/lib/crc32.c  fw_env.c  fw_env_main.c
-HOSTSRCS += $(SRCTREE)/lib/ctype.c $(SRCTREE)/lib/linux_string.c
-HOSTSRCS += $(SRCTREE)/common/env_attr.c $(SRCTREE)/common/env_flags.c
-HEADERS	:= fw_env.h $(OBJTREE)/include/config.h
-
 # Compile for a hosted environment on the target
-HOSTCPPFLAGS  = -idirafter $(SRCTREE)/include \
+HOST_EXTRACFLAGS  = -idirafter $(SRCTREE)/include \
 		-idirafter $(SRCTREE)/arch/$(ARCH)/include \
 		-idirafter $(OBJTREE)/include \
 		-idirafter $(SRCTREE)/tools/env \
@@ -21,23 +14,12 @@
 		-DTEXT_BASE=$(TEXT_BASE)
 
 ifeq ($(MTD_VERSION),old)
-HOSTCPPFLAGS += -DMTD_OLD
+HOST_EXTRACFLAGS += -DMTD_OLD
 endif
 
-all:	$(obj)fw_printenv
-
-# Some files complain if compiled with -pedantic, use HOSTCFLAGS_NOPED
-$(obj)fw_printenv:	$(HOSTSRCS) $(HEADERS)
-	$(HOSTCC) $(HOSTCFLAGS_NOPED) $(HOSTLDFLAGS) -o $@ $(HOSTSRCS)
-	$(HOSTSTRIP) $@
-
-clean:
-	rm -f $(obj)fw_printenv
-
-#########################################################################
-
-include $(TOPDIR)/rules.mk
-
-sinclude $(obj).depend
+hostprogs-y := fw_printenv
+always := $(hostprogs-y)
 
-#########################################################################
+fw_printenv-objs := fw_env.o fw_env_main.o \
+	crc32.o ctype.o linux_string.o \
+	env_attr.o env_flags.o