Implement DfuSe extensions.

[oskirby]

STMicro has an extended DFU protocol that allows upload an download to arbitrary addresses, mass erases and other such commands by overloading the wValue field in DFU_DNLOAD and DFU_UPLOAD commands. This might be handy to implement to allow users to write images specific locations within the user partition.

See: https://www.st.com/resource/en/application_note/cd00264379-usb-dfu-protocol-used-in-the-stm32-bootloader-stmicroelectronics.pdf