Default to extended-remote instead of remote mode

Extended remote allows a lot more features like attaching and detaching and much more fine-grained execution options. If a gdbserver implementation supports it (and OpenOCD sure does) it should be preferred over `remote`.

Author: therealprof

openocd.gdb

@@ -1,4 +1,4 @@
-target remote :3333
+target extended-remote :3333
 
 # print demangled symbols
 set print asm-demangle on
@@ -29,4 +29,4 @@ monitor arm semihosting enable
 load
 
 # start the process but immediately halt the processor
-stepi
+stepi