platforms/f3: moved the linker script and fixed the build system

We need build the right libopencm3 library which is not done by default, so this adds an extra build step for it

src/platforms/f3/Makefile.inc

@@ -8,7 +8,7 @@ CFLAGS += -Istm32/include -mcpu=cortex-m4 -mthumb \
 	-DDFU_SERIAL_LENGTH=13 -Iplatforms/stm32
 
 LDFLAGS =  --specs=nano.specs -lopencm3_stm32f3 \
-	-Wl,-T,platforms/f3-if/stm32f303xc.ld -nostartfiles -lc -lnosys \
+	-Wl,-T,platforms/stm32/stm32f303xc.ld -nostartfiles -lc -lnosys \
 	-Wl,-Map=mapfile -mthumb -mcpu=cortex-m4 -Wl,-gc-sections \
 	-mfloat-abi=hard -mfpu=fpv4-sp-d16 \
 	-L../libopencm3/lib
@@ -24,6 +24,12 @@ SRC += 	cdcacm.c	\
 	timing_stm32.c	\
 
 all:	blackmagic.bin
+blackmagic.elf: libopencm3_stm32f3
+
+libopencm3_stm32f3:
+	$(Q)$(MAKE) $(MFLAGS) -C ../libopencm3 lib/stm32/f3
 
 host_clean:
 	-$(Q)$(RM) blackmagic.bin
+
+.PHONY: libopencm3_stm32f3