Add install-headers target

Install the libopenbmc_intf includes in prep for a devel
package.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/libopenbmc_intf/Makefile b/libopenbmc_intf/Makefile
index 8853318..54bef57 100644
--- a/libopenbmc_intf/Makefile
+++ b/libopenbmc_intf/Makefile
@@ -1,14 +1,19 @@
 PACKAGE_DEPS=gio-unix-2.0 glib-2.0
-INSTALLDEPS=install-lib
+INSTALLDEPS=install-lib install-headers
 CLEANDEPS=clean-lib
 DEFAULT_ALL=$(LIBOBMC)
 ALL_CFLAGS+=-iquote ../gdbus
 LIBOBMC=openbmc_intf
+INCLUDES=openbmc_intf.h openbmc.h gpio.h
 
 $(LIBOBMC): %: %.o gpio.o
 	$(CC) -shared $(CFLAGS) $(LDFLAGS) -Wl,-soname,lib$(LIBOBMC).so \
 		-o lib$@.so.1 $^ $(LDLIBS)
 
+install-headers:
+	@mkdir -p $(DESTDIR)$(includedir)
+	install $(INCLUDES) $(DESTDIR)$(includedir)
+
 install-lib:
 	@mkdir -p $(DESTDIR)$(libdir)
 	install lib$(LIBOBMC).so.1 $(DESTDIR)$(libdir)