Update analyzer descriptors and request handling

[martinling]

This PR updates the analyzer gateware's descriptors and request handling as per recent discussions.

The changes are as follows:

Device descriptor:

• Changed manufacturer string from LUNA to Cynthion Project.
• Set serial string from ECP5 configuration flash ID.
• Set bcdVersion to platform version rather than analyzer protocol version.

Interface descriptor:

• Set bInterfaceClass to 0xFF (vendor specific).
• Set bInterfaceSubclass and bInterfaceProtocol to values specified in cynthion.shared.

Request handler:

• Now accepts requests with the recipient as the interface, rather than the device.

Corresponding Packetry support is in https://github.com/greatscottgadgets/packetry/pull/93.

[martinling]

Just realised that the bcdVersion usage here isn't consistent with Apollo. Cynthion r1.4 should be encoded as 1.04, not 1.40. I'll fix that.

[martinling]

Fixed. Now stores the version as a tuple on the platforms, and converts to the appropriate form when setting bcdDevice.

[martinling]

Rebased now that #86 is merged, so that bInterfaceProtocol version starts at 0x00.