frv: extend gdbstub to support more features of gdb

frv: extend gdbstub to support more features of gdb

Extend gdbstub to support more features of gdb remote protocol to keep
gdb-7 and emacs gud mode happy:

 (*) The D command.  Detach debugger.

 (*) The H command.  Handle setting the target thread by ignoring it.

 (*) The qAttached command.  Indicate we 'attached' to an existing process.

 (*) The qC command.  Indicate that the current thread ID is 0.

 (*) The qOffsets command.  Indicate that no relocation has been done.

 (*) The qSymbol:: command.  Indicate that we're not interested in looking up
     any symbol addresses.

 (*) The qSupported command.  Indicate the maximum packet size and the fact
     that reverse step and continue aren't supported.

 (*) The vCont? command.  Indicate that we don't support any of its variants.

Also make it possible to trace the commands and replies without tracing
the individual character I/O.

[[email protected]: make gdbstub_handle_query() static]
Signed-off-by: David Howells <[email protected]>
Cc: Jason Wessel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>