Drop newlib printf: log via BDK s_vprintf, add debug.ini log switch

log_write was the only vsnprintf user and pulled in newlib's printf,
dtoa, malloc and soft-float code (~44 KB). The payload now fits the
RCM limit again (146800 -> 102801 bytes); the build fails if it grows
past it. debug.ini log=1 writes sd:/config/omninx/install.log.

Makefile

@@ -60,7 +60,7 @@ OBJS_RAMTEST := $(filter-out $(BUILDDIR)/$(TARGET)/main.o,$(OBJS)) \
 all: $(OUTPUTDIR)/$(OUTPUT_NAME)
 	$(eval BIN_SIZE = $(shell wc -c < $(OUTPUTDIR)/$(OUTPUT_NAME)))
 	@echo "Payload size is $(BIN_SIZE) bytes (max $(MAX_PAYLOAD_SIZE) for RCM)"
-	@if [ $(BIN_SIZE) -gt $(MAX_PAYLOAD_SIZE) ]; then echo "WARNING: payload exceeds the RCM size limit"; fi
+	@if [ $(BIN_SIZE) -gt $(MAX_PAYLOAD_SIZE) ]; then echo "ERROR: payload exceeds the RCM size limit"; exit 1; fi
 
 clean:
 	@rm -rf $(BUILDDIR)