tools/gpio: add install section

Allow user to call install target.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/tools/gpio/Makefile b/tools/gpio/Makefile
index 5a82f15..250a891 100644
--- a/tools/gpio/Makefile
+++ b/tools/gpio/Makefile
@@ -1,5 +1,7 @@
 include ../scripts/Makefile.include
 
+bindir ?= /usr/bin
+
 ifeq ($(srctree),)
 srctree := $(patsubst %/,%,$(dir $(shell pwd)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
@@ -62,6 +64,12 @@
 	rm -f $(OUTPUT)include/linux/gpio.h
 	find $(if $(OUTPUT),$(OUTPUT),.) -name '*.o' -delete -o -name '\.*.d' -delete
 
+install: $(ALL_PROGRAMS)
+	install -d -m 755 $(DESTDIR)$(bindir);		\
+	for program in $(ALL_PROGRAMS); do		\
+		install $$program $(DESTDIR)$(bindir);	\
+	done
+
 FORCE:
 
-.PHONY: all clean FORCE prepare
+.PHONY: all install clean FORCE prepare