scons: Rearrange functions to be next to the code that uses them.
scons: Rearrange functions to be next to the code that uses them.

The code which generated SimObject related param wrappers, cxx wrappers,
enum headers, etc was organized strangely. All the functions which
were used as SCons Actions were listed next to each other, and then all
the code which would set up each of those types of files and actually
use the Actions were next to each other.

This change rearranges that code so that the Action function is
immediately before the code which applies it. Or in other words, this
section of the SConscript is now grouped by the files being created,
rather than the type of the piece of machinery being defined to do that.

Change-Id: Ideee7bd44dac89c51840ec5970d95f6ccbbd1c8f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49402
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>

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