usbdebug: Improve receive speed

Read from USB endpoint_in 8 bytes at a time, the maximum what
EHCI debug port capability has to offer.

Change-Id: I3d012d758a24b24f894e587b301f620933331407
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/4700
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/console/usbdebug_console.c

@@ -34,12 +34,7 @@ static void dbgp_tx_byte(unsigned char data)
 
 static unsigned char dbgp_rx_byte(void)
 {
-	unsigned char data = 0xff;
-
-	if (dbgp_ep_is_active(dbgp_console_input()))
-		dbgp_bulk_read_x(dbgp_console_input(), &data, 1);
-
-	return data;
+	return usbdebug_rx_byte(dbgp_console_input());
 }
 
 static void dbgp_tx_flush(void)