simplify board API, adding stm32f3 discovery

- remove board header since it is not used

hw/bsp/stm32f303disc/board.mk

@@ -0,0 +1,37 @@
+CFLAGS += \
+	-DHSE_VALUE=8000000 \
+	-DCFG_TUSB_MCU=OPT_MCU_STM32F3 \
+	-DSTM32F303xC \
+	-mthumb \
+	-mabi=aapcs-linux \
+	-mcpu=cortex-m4 \
+	-mfloat-abi=hard \
+	-mfpu=fpv4-sp-d16 \
+	-nostdlib -nostartfiles
+
+# All source paths should be relative to the top level.
+LD_FILE = hw/bsp/stm32f303disc/STM32F303VCTx_FLASH.ld
+
+LDFLAGS += -mthumb -mcpu=cortex-m4
+
+SRC_C += \
+	hw/mcu/st/system-init/system_stm32f3xx.c
+
+SRC_S += \
+	hw/mcu/st/startup/stm32f3/startup_stm32f303xc.s
+
+INC += \
+	-I$(TOP)/hw/mcu/st/stm32lib/CMSIS/STM32F3xx/Include \
+	-I$(TOP)/hw/mcu/st/cmsis
+
+VENDOR = st
+CHIP_FAMILY = stm32f4
+
+JLINK_DEVICE = stm32f303vc
+
+# Path to STM32 Cube Programmer CLI, should be added into system path 
+STM32Prog = STM32_Programmer_CLI
+
+# flash target using on-board stlink
+flash: $(BUILD)/$(BOARD)-firmware.elf
+	$(STM32Prog) --connect port=swd --write $< --go