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/kernel-doc/Makefile b/tools/kernel-doc/Makefile
index eb56e2e..f15a4b7 100644
--- a/tools/kernel-doc/Makefile
+++ b/tools/kernel-doc/Makefile
@@ -4,22 +4,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-include $(TOPDIR)/config.mk
-
-all:	$(obj)docproc
-
-$(obj)docproc:	docproc.c
-	$(HOSTCC) $(HOSTCFLAGS) $(HOSTLDFLAGS) -o $@ $^
-	$(HOSTSTRIP) $@
-
-clean:
-	rm -rf docproc
-
-#########################################################################
-
-# defines $(obj).depend target
-include $(SRCTREE)/rules.mk
-
-sinclude $(obj).depend
+hostprogs-y := docproc
+always := $(hostprogs-y)
 
-#########################################################################
+HOST_EXTRACFLAGS := -pedantic