arm: working bootloader, example app

'make' will produce two outputs:
- bootloader.elf to be loaded into the bitstream
- app.bin to be loaded through the programmer

Loading app.bin is as simple as:
- reset the board
- `python3 prog.py app.bin`

arm/makefile

@@ -11,7 +11,7 @@ CFLAGS = -march=armv6-m -g -ffunction-sections -fdata-sections -O2 -Werror -Wall
 CXXFLAGS = $(CFLAGS) -std=c++20 -fno-exceptions
 LDFLAGS = -march=armv6-m \
 		  -g --specs=nano.specs --specs=nosys.specs \
-		  -Wl,--gc-sections -Wl,-T$(linker_script) -O2 \
+		  -Wl,--gc-sections -O2 \
 		  -Wl,--print-memory-usage
 
 sources += hal/lib/common/xil_assert.c
@@ -20,21 +20,25 @@ includes += -Ihal/lib/common
 sources += hal/uart/xuartlite.c hal/uart/xuartlite_stats.c
 includes += -Ihal/uart
 
-objects = main.o vector_table.o $(sources:.c=.o)
+bootloader_objects = uart.o bootloader.o vector_table.o $(sources:.c=.o)
+app_objects = app_init.o main.o
 
 CFLAGS += $(includes)
 
-all: bootloader.elf
+all: bootloader.elf app.bin
 
 %.bin: %.elf
 	$(OBJCOPY) -O binary $< $@
 
-bootloader.elf: $(objects)
+bootloader.elf: $(bootloader_objects)
+	$(LD) -Wl,-Tbootloader.ld $(LDFLAGS) -o $@ $^
+
+app.elf: $(app_objects)
 
 %.elf:
-	$(LD) $(LDFLAGS) -o $@ $^
+	$(LD) -Wl,-Tapp.ld $(LDFLAGS) -o $@ $^
 
 .PHONY: clean
 
 clean:
-	rm -rf *.elf *.bin $(objects)
+	rm -rf *.elf *.bin $(app_objects) $(bootloader_objects)