Support for STM32H503 MCU

- added support for STM32H503RB on H503RB-NUCLEO board
- modified H5 family.c file to allow portability between H503 and H565/H573
- redefined USB_DRD_BASE to USB_DRD_FS_BASE if STM32H503xx is used

hw/bsp/stm32h5/boards/stm32h503nucleo/board.cmake

@@ -0,0 +1,8 @@
+set(MCU_VARIANT stm32h503xx)
+set(JLINK_DEVICE stm32h503rb)
+
+function(update_board TARGET)
+  target_compile_definitions(${TARGET} PUBLIC
+    STM32H503xx
+    )
+endfunction()