arch: Minor cleanup of imports in isa_parser.py.

arch: Minor cleanup of imports in isa_parser.py.

The with statement and print function are no longer in the future, and
the "inspect" module is not used. Also alphabetize the imports.

Change-Id: I35f2b7b0f7495cb9ca79d2cbe05f020560ec3593
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35280
Reviewed-by: Steve Reinhardt <stever@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>