RNN support (part 1)
Created by: vloncar
As discussed before, this is the first stage of the RNN support. The PR includes the support for parsing RNN layers into the IR, as well as the Vivado-specific initialization. The same initialization specific to Quartus backend can be part of the second PR. After this is merged, parts 2 and 3 will add HLS implementations for Vivado and Quartus.