RPC interface: move all references to CRpcIo pointers back into
rpc_calls.h and only return string identifiers for both interfaces
and devices to the HAL. Hopefully this solves the Windows build
issues mentioned in #251.
To do: clean up this part if the code, simplify, remove unneeded
RPC functions in CTestboard (e.g. selecting IF via CRpcIo pointer)
Uncomment call to SelectInterface(string) in case we found the
requested DTB
Add some debug comment beef