base: adding support for O packet

O packet allow the GDB stub to send a message to display for the GDB
remote.
This function could be used to implement certains specific command
response.

Change-Id: I1c9a1ca956efcf19c93a8503d97c1fb27f555966
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63529
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed