Adding ability to clear lm32 in SPI flash.

Current loading lm32 firmware from SPI flash is broken because it gets loaded
into main ram and that doesn't work (see issue timvideos#274).

Author: mithro

Makefile

@@ -153,7 +153,7 @@ load: load-gateware $(addprefix load-,$(TARGETS))
 flash-gateware: gateware-submodules
 	$(MAKEPY_CMD) flash-bitstream
 
-flash: flash-gateware  $(addprefix flash-,$(TARGETS))
+flash: flash-gateware $(addprefix flash-,$(TARGETS))
 	@echo ""
 	@echo ""
 	@echo "Power cycle your board to boot newly flashed stuff."

Makefile.lm32

@@ -68,6 +68,11 @@ flash-lm32: image-lm32
 	echo "Flashing to $$($(PYTHON) -c "print(hex($$FIRMWARE_ADDRESS))") ($$FIRMWARE_ADDRESS)"; \
 	$(FLASHEXTRA_CMD) $(HDMI2USBDIR)/firmware/lm32/firmware.fbi $$FIRMWARE_ADDRESS
 
+clear-flash-lm32:
+	export FIRMWARE_ADDRESS=$$($(PYTHON) -c "import platforms.$(BOARD) as b; print(b.Platform.gateware_size)"); \
+	echo "Zeroing $$($(PYTHON) -c "print(hex($$FIRMWARE_ADDRESS))") ($$FIRMWARE_ADDRESS)"; \
+	$(FLASHEXTRA_CMD) $(HDMI2USBDIR)/firmware/zero.bin $$FIRMWARE_ADDRESS
+
 clean-lm32:
 	if [ -f $(MSCDIR)/software/include/generated/cpu.mak ]; then \
 		$(MAKE) -C firmware/lm32 clean; \