Fix wrapper.exp testcase with stdio gdbserver.

Fix wrapper.exp testcase with stdio gdbserver.

	* lib/gdbserver-support.exp (gdbserver_default_get_remote_address):
	Add comment.
	(gdbserver_default_get_comm_port): New function.
	(gdbserver_start): Check if board file provided
	"gdbserver,get_comm_port" and use it if so.
	* boards/native-stdio-gdbserver.exp (sockethost): Set to "".
	(gdb,socketport): Set to "stdio".
	(gdbserver,get_comm_port): Set to ${board}_get_comm_port.
	(stdio_gdbserver_template): Delete.
	(${board}_get_remote_address): Update.
	(${board}_build_remote_cmd): Delete.
	(${board}_get_comm_port): New function.
	(${board}_spawn): Update.
	* boards/remote-stdio-gdbserver.exp (${board}_build_remote_cmd):
	Delete.
	(${board}_get_remote_address): Update.
	(${board}_get_comm_port): New function.