That header has 3.3v, ground, data in and out. It doesn't have any other signaling pins. If you want flow control I believe you can pull them off the unpopulated U15 pads if you change some pin configuration. Pins 5 and 6 of that look like they're configured to be I2C SDA and SCK, but since they go back to MPP and MPP they can be reconfigured as RTS and CTS. However, that would require opening the plug and soldering wires to it.
MPP and MPP can also be configured to be RTS and CTS, but those are being used as bits 2 and 3 of the microSD card data pins.
The table that has what pins can do what is on page 53 of the processor's hardware manual