rtos: support gdb_get_register_packet

This patch adds support for p packet responses by targets configured
with RTOS support. This change required moving to a rtos_reg struct,
which is similar to struct reg used by targets, which resulted in
needing to update each stacking with register numbers. This patch also
allows targets with non-linear register numbers to function with RTOSes
as well.

Change-Id: I5b189d74110d6b6f2fa851a67ab0762ae6b1832f
Signed-off-by: Steven Stallion <stallion@squareup.com>
Reviewed-on: http://openocd.zylin.com/4121
Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>

src/server/gdb_server.c

@@ -1301,6 +1301,9 @@ static int gdb_get_register_packet(struct connection *connection,
 	LOG_DEBUG("-");
 #endif
 
+	if ((target->rtos != NULL) && (ERROR_OK == rtos_get_gdb_reg(connection, reg_num)))
+		return ERROR_OK;
+
 	retval = target_get_gdb_reg_list(target, &reg_list, &reg_list_size,
 			REG_CLASS_ALL);
 	if (retval != ERROR_OK)