GDB Python rtems.pprinter is missing

Summary

There is a module missing from the RTEMS GDB C++ Pretty Printer support. Starting gdb results in:

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Reading symbols from build/arm-rtems6-xilinx_zynq_microzed/app/spu/spu...
RTEMS GDB Support
Python Exception <class 'ModuleNotFoundError'>: No module named 'rtems.pprinter'
(gdb)

This issue is set to the %6.1 milestone because it is fixing the support being documented by rtems/rtos/rtems-release!9 (merged).

Steps to reproduce

Start an RTEMS gdb with an RTEMS executable.