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

fastboot/fastboot_protocol.txt

@@ -12,8 +12,8 @@ Basic Requirements
 ------------------
 
 * Two bulk endpoints (in, out) are required
-* Max packet size must be 64 bytes for full-speed and 512 bytes for 
-  high-speed USB
+* Max packet size must be 64 bytes for full-speed, 512 bytes for
+  high-speed and 1024 bytes for Super Speed USB.
 * The protocol is entirely host-driven and synchronous (unlike the
   multi-channel, bi-directional, asynchronous ADB protocol)
 

fastboot/protocol.c

@@ -216,7 +216,7 @@ int fb_download_data(usb_handle *usb, const void *data, unsigned size)
     }
 }
 
-#define USB_BUF_SIZE 512
+#define USB_BUF_SIZE 1024
 static char usb_buf[USB_BUF_SIZE];
 static int usb_buf_len;