python: Add a mechanism for installing pybind modules.
python: Add a mechanism for installing pybind modules.

pybind provides a mechanism for this already, but it assumes that
because it works through static initializers, it must run before the
python interpreter has started. That is not true when gem5 is built as a
library, since its static intitializers won't run until that library is
loaded.

Change-Id: I6f36c5f3831dda893039b4923902e9ce46a91808
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54003
Maintainer: Bobby Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Bobby Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54263

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5