Allow transports to override the selected target (hla configs unification)

This should allow to share common configs for both regular access and
high-level adapters.

Use the newly-added functionality in stlink and icdi drivers, amend
the configs accordingly.

Runtime-tested with a TI tm4c123g board.

Change-Id: Ibb88266a4ca25f06f6c073e916c963f017447bad
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
[gus@projectgus.com: context-specific deprecation warnings]
Signed-off-by: Angus Gratton <gus@projectgus.com>
[andrew.smirnov@gmail.com: additional nrf51.cfg mods]
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Tested-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Reviewed-on: http://openocd.zylin.com/1664
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

src/transport/transport.h

@@ -65,6 +65,14 @@ struct transport {
 	 */
 	int (*init)(struct command_context *ctx);
 
+	/**
+	 * Optional. If defined, allows transport to override target
+	 * name prior to initialisation.
+	 *
+	 * @returns ERROR_OK on success, or an error code on failure.
+	 */
+	int (*override_target)(const char **targetname);
+
 	/**
 	 * Transports are stored in a singly linked list.
 	 */