bsps/nio2/*: Add SPDX for RTEMS legacy license

These may still be relicensed but adding SPDX is needed.

Updates #4805.

bsps/nios2/nios2_iss/btimer/btimer.c

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0+-with-RTEMS-exception */
+
 /*
  * This file manages the benchmark timer used by the RTEMS Timing Test
  * Suite.  Each measured time period is demarcated by calls to

bsps/nios2/nios2_iss/console/console.c

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0+-with-RTEMS-exception */
+
 /*
  *  This file implements simple console IO via JTAG UART.
  */

bsps/nios2/nios2_iss/start/bspstart.c

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0+-with-RTEMS-exception */
+
 /*
  *  This routine starts the application.  It includes application,
  *  board, and monitor specific initialization and configuration.

bsps/nios2/nios2_iss/start/crtnn.S

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0+-with-RTEMS-exception */
+
 /*  NIOS2 crtn.asm fix
  *
  *  COPYRIGHT (c) 2005-2006 Kolja Waschk rtemsdev/ixo.de

bsps/nios2/nios2_iss/start/main.c

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0+-with-RTEMS-exception */
+
 /*  main()
  *
  *  This is the entry point for the application.  It calls

bsps/nios2/nios2_iss/start/start.S

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0+-with-RTEMS-exception */
+
 /*  NIOS2 startup code
  *
  *  This is the entry point on reset and when loading the