tools: usb: move to tools buildsystem

Converting the Makefile to use the new tools buildsystem.
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
[fixes builds with O=...]
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20200819071733.60028-1-heikki.krogerus@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/usb/Build

+testusb-y += testusb.o
+ffs-test-y += ffs-test.o

tools/usb/Makefile

 # SPDX-License-Identifier: GPL-2.0
 # Makefile for USB tools
+include ../scripts/Makefile.include
 
-PTHREAD_LIBS = -lpthread
-WARNINGS = -Wall -Wextra
-CFLAGS = $(WARNINGS) -g -I../include
-LDFLAGS = $(PTHREAD_LIBS)
+bindir ?= /usr/bin
 
-all: testusb ffs-test
-%: %.c
-	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+ifeq ($(srctree),)
+srctree := $(patsubst %/,%,$(dir $(CURDIR)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+endif
+
+# Do not use make's built-in rules
+# (this improves performance and avoids hard-to-debug behaviour);
+MAKEFLAGS += -r
+
+override CFLAGS += -O2 -Wall -Wextra -g -D_GNU_SOURCE -I$(OUTPUT)include -I$(srctree)/tools/include
+override LDFLAGS += -lpthread
+
+ALL_TARGETS := testusb ffs-test
+ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS))
+
+all: $(ALL_PROGRAMS)
+
+export srctree OUTPUT CC LD CFLAGS
+include $(srctree)/tools/build/Makefile.include
+
+TESTUSB_IN := $(OUTPUT)testusb-in.o
+$(TESTUSB_IN): FORCE
+	$(Q)$(MAKE) $(build)=testusb
+$(OUTPUT)testusb: $(TESTUSB_IN)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
+
+FFS_TEST_IN := $(OUTPUT)ffs-test-in.o
+$(FFS_TEST_IN): FORCE
+	$(Q)$(MAKE) $(build)=ffs-test
+$(OUTPUT)ffs-test: $(FFS_TEST_IN)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
 
 clean:
-	$(RM) testusb ffs-test
+	rm -f $(ALL_PROGRAMS)
+	find $(if $(OUTPUT),$(OUTPUT),.) -name '*.o' -delete -o -name '\.*.d' -delete -o -name '\.*.o.cmd' -delete
+
+install: $(ALL_PROGRAMS)
+	install -d -m 755 $(DESTDIR)$(bindir);		\
+	for program in $(ALL_PROGRAMS); do		\
+		install $$program $(DESTDIR)$(bindir);	\
+	done
+
+FORCE:
+
+.PHONY: all install clean FORCE prepare