defconfig: sdxprairie: Enable burst flow control

Enable data flow control so that grant indications can limit and control
the number of packets to be sent to modem.

Change-Id: Iaa768e037d3a1d27a71732b4e15ea63366cacc4b
Acked-by: Ning Cai <ncai@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>