Good catch Prad.
Further review of the TLK110 documentation reveals that although it does provide a 50MHz clock output, it cannot be used to actually clock the RMII interface, so in the case of TLK110 you would need to use an external 50MHz oscillator as discussed previously.
I have an email in to the TLK team to verify this...but for now I think it safe to assume that the external oscillator is required for TLK110.