misc: updated shabang for python script

The default python on MacOS doesn’t have an alias to python2.
The official python version supported in gem5 is Python2.7.

This patch updates the shabang according to the version required in gem5.

Change-Id: I9533c0f7858b5b3cab0ef101be1ee5cd718105b0
Reviewed-on: https://gem5-review.googlesource.com/c/15375
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

style: change C/C++ source permissions to noexec

Several files in the repository were tracked with execute permissions
even though the files are just normal C/C++ files (and the one .isa).

Change-Id: I976b096acab4a1fc74c5699ef1f9b222c1e635c2
Reviewed-on: https://gem5-review.googlesource.com/7241
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

misc: Update #!env calls for python to explicit version

In some newer Linux distributions, env python default to Python 3.0. This
patch explicitly uses "python2" instead of just "python" for all scripts
that use #!

Reported-by: Sanchayan Maity <maitysanchayan@gmail.com>
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>

ext: Add a McPAT regression tester
Add a regression tester to McPAT. Joel Hestness wrote these tests and Yasuko
Eckert modified them to reflect the new McPAT interface and other changes
the previous patch made.

ext: McPAT interface changes and fixes
This patch includes software engineering changes and some generic bug fixes
Joel Hestness and Yasuko Eckert made to McPAT 0.8. There are still known
issues/concernts we did not have a chance to address in this patch.

High-level changes in this patch include:
1) Making XML parsing modular and hierarchical:
- Shift parsing responsibility into the components
- Read XML in a (mostly) context-free recursive manner so that McPAT input
files can contain arbitrary component hierarchies
2) Making power, energy, and area calculations a hierarchical and recursive
process
- Components track their subcomponents and recursively call compute
functions in stages
- Make C++ object hierarchy reflect inheritance of classes of components
with similar structures
- Simplify computeArea() and computeEnergy() functions to eliminate
successive calls to calculate separate TDP vs. runtime energy
- Remove Processor component (now unnecessary) and introduce a more abstract
System component
3) Standardizing McPAT output across all components
- Use a single, common data structure for storing and printing McPAT output
- Recursively call print functions through component hierarchy
4) For caches, allow splitting data array and tag array reads and writes for
better accuracy
5) Improving the usability of CACTI by printing more helpful warning and error
messages
6) Minor: Impose more rigorous code style for clarity (more work still to be
done)
Overall, these changes greatly reduce the amount of replicated code, and they
improve McPAT runtime and decrease memory footprint.

ext: change McPAT to not force compile in 32-bit mode.

ext: Redirect McPAT object files

All object files and McPAT binaries are moved to directory gem5/build/mcpat/
rather than creating them locally.

ext: add McPAT source

this patch adds the source for mcpat, a power, area, and timing modeling
framework.