Merge pull request #1855 from Guozhanxin/master

[bsp][hifive1] add Makefile file

bsp/hifive1/Makefile

@@ -0,0 +1,7 @@
+scons := python ${SCONS}\scons.py
+
+all:
+	@$(scons)
+
+clean:
+	@$(scons) -c