add CH32V20x USB OTG/FS driver

hw/bsp/ch32v307/family.mk

@@ -4,6 +4,9 @@
 # Toolchain from https://github.com/xpack-dev-tools/riscv-none-embed-gcc-xpack
 CROSS_COMPILE ?= riscv-none-embed-
 
+# Toolchain from https://github.com/xpack-dev-tools/riscv-none-elf-gcc-xpack
+#CROSS_COMPILE ?= riscv-none-elf-
+
 # Submodules
 CH32V307_SDK = hw/mcu/wch/ch32v307
 
@@ -13,6 +16,8 @@ CH32V307_SDK_SRC = $(CH32V307_SDK)/EVT/EXAM/SRC
 include $(TOP)/$(BOARD_PATH)/board.mk
 CPU_CORE ?= rv32imac-ilp32
 
+# 	-march=rv32imac_zicsr
+
 CFLAGS += \
 	-flto \
 	-msmall-data-limit=8 \