cpu: Narrow the dependencies of the StaticInst class.
cpu: Narrow the dependencies of the StaticInst class.

Include only the minimal number of headers to make StaticInst subclasses
easier to test with unit tests.

Change-Id: Ie2e1c01b77d1776b366d29982e481d62b6a2b8cf
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42965
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Daniel Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>

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