Update 4.11 RSB to work with python 3 and python 2

[chrisj at rtems.org]

Hello,

This change backports the RSB python source from master to 4.11 so
4.11 can be maintained on newer hosts.

GDB has been updated to 9.1 for the architectures that can support it.
The SPARC architecture has been lift at 7.9 with building with python
been disabled.

Builds on Ubuntu 20 and FreeBSD. FreeBSD has been tested with
Python 2 and Python 3

Chris