Add variable to control what program gets flashed to FPGA.

fpga/e300artydevkit/Makefile

@@ -4,6 +4,10 @@ VIVADOFLAGS := \
 	-source script/board.tcl \
 	-source script/prologue.tcl
 
+# Path to a program in raw binary format to be flashed into the address that the
+# bootrom jumps to.
+FLASHED_PROGRAM ?=
+
 bit := obj/system.bit
 $(bit): script/impl.tcl  script/init.tcl
 	VSRC_TOP=$(VSRC_TOP) EXTRA_VSRCS="$(EXTRA_VSRCS)" $(VIVADO) $(VIVADOFLAGS) -source script/init.tcl -source script/impl.tcl
@@ -13,7 +17,7 @@ bit: $(bit)
 
 mcs := obj/system.mcs
 $(mcs): $(bit)
-	$(VIVADO) $(VIVADOFLAGS) script/cfgmem.tcl -tclargs $@ $^
+	$(VIVADO) $(VIVADOFLAGS) script/cfgmem.tcl -tclargs $@ $^ $(FLASHED_PROGRAM)
 
 .PHONY: mcs
 mcs: $(mcs)