Implemented changes suggested in the review:
- restored original name of SystemClock_Config() function
- some GPIO clocks are only enabled if macros are defined
- moved GPIO clocks init back to family.c
- 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
hathach