selftests: gpio: restructure Makefile

This patch cleans up the Makefile by restructuring a couple of
things, namely:
1) change explicit paths in targets for variables
2) substitute a variable (BINARIES) for another, part of the
selftests build system (TEST_PROGS_EXTENDED)
3) proper cleaning up of the EXTRA objects

The resulting Makefile is much more readable and manageable.

Signed-off-by: Fathi Boudra <[e-mail]>
Signed-off-by: Daniel Díaz <[e-mail]>
Signed-off-by: Shuah Khan (Samsung OSG) <[e-mail]>

tools/testing/selftests/gpio/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 
-TEST_PROGS := gpio-mockup.sh
-TEST_FILES := gpio-mockup-sysfs.sh $(BINARIES)
-BINARIES := gpio-mockup-chardev
-EXTRA_PROGS := ../gpiogpio-event-mon ../gpiogpio-hammer ../gpiolsgpio
-EXTRA_DIRS := ../gpioinclude/
-EXTRA_OBJS := ../gpiogpio-event-mon-in.o ../gpiogpio-event-mon.o
-EXTRA_OBJS += ../gpiogpio-hammer-in.o ../gpiogpio-utils.o ../gpiolsgpio-in.o
-EXTRA_OBJS += ../gpiolsgpio.o
-
-include ../lib.mk
-
-all: $(BINARIES)
-
-override define CLEAN
-	$(RM) $(BINARIES) $(EXTRA_PROGS) $(EXTRA_OBJS)
-	$(RM) -r $(EXTRA_DIRS)
-endef
-
 CFLAGS += -O2 -g -std=gnu99 -Wall -I../../../../usr/include/
 LDLIBS += -lmount -I/usr/include/libmount
 
-$(BINARIES):| khdr
-$(BINARIES): ../../../gpio/gpio-utils.o
+TEST_PROGS := gpio-mockup.sh
+TEST_FILES := gpio-mockup-sysfs.sh
+TEST_PROGS_EXTENDED := gpio-mockup-chardev
 
-../../../gpio/gpio-utils.o:
-	make ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) -C ../../../gpio
+GPIODIR := ../../../gpio
+GPIOOBJ := gpio-utils.o
+
+include ../lib.mk
+
+all: $(TEST_PROGS_EXTENDED)
+
+override define CLEAN
+	$(RM) $(TEST_PROGS_EXTENDED)
+	$(MAKE) -C $(GPIODIR) clean
+endef
+
+$(TEST_PROGS_EXTENDED):| khdr
+$(TEST_PROGS_EXTENDED): $(GPIODIR)/$(GPIOOBJ)
+
+$(GPIODIR)/$(GPIOOBJ):
+	$(MAKE) -C $(GPIODIR)