Makefile: Better display of size (device memory usage)

Run avr-size with the --mcu=... -C option as well.  That reports how
much actual device program and data memory is used along with a
percentage fullness.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

Marlin/Makefile

 
 	# Display size of file.
 HEXSIZE = $(SIZE) --target=$(FORMAT) applet/$(TARGET).hex
-ELFSIZE = $(SIZE)  applet/$(TARGET).elf
+ELFSIZE = $(SIZE) --mcu=$(MCU) -C applet/$(TARGET).elf; \
+          $(SIZE)  applet/$(TARGET).elf
 sizebefore:
 	$P if [ -f applet/$(TARGET).elf ]; then echo; echo $(MSG_SIZE_BEFORE); $(HEXSIZE); echo; fi