drivers: usb: xhci-fsl: Change burst beat and outstanding pipelined transfers requests

This is required for better performance, and performs below tuning:
1. Enable burst length set, and define it as 4/8/16.
2. Set burst request limit to 16 requests.

Signed-off-by: Rajesh Bhagat <rajesh.bhagat@nxp.com>
Signed-off-by: Sriram Dash <sriram.dash@nxp.com>