ECP5 support and DFU+CDC support

[emard]

HI

I have hacked something with ECP5 staring from hadbadge
version, and would like to have your "official" ECP5 support.

Problem with hadbadge version I ported is that it sometimes doesn't
enumerate when plugged, and re-plug makes it. I see no issues
so I guess no2usb and no2bootloader are 100% reliable at plugging :)

Also it would be great if dual USB function can be somehow
supported so that core either alone or with some riscv fw
enumerates both as DFU and CDC USB-serial.
CDC with TX/RX and few other RS232 lines can be user
console and programmer for onboard ESP32.