system: core: fastboot: Increase USB protocol buffer size to 1024

With USB3.0 SS support the max packet size supported by USB protocol
is 1024 bytes. When connected to a USB device in SuperSpeed, if only
512 bytes are sent at a time the device would interpret each transfer
as a short packet and slows down overall throughput. To accommodate
for SuperSpeed USB bulk endpoints, increase the buffer size to 1024.

Change-Id: I4f447fe38045bc0008e2d6dd3f36c2d6819d6c15