base: Teach the socket listeners how to bind to the loopback.

The loopback device will allow access to various services like remote GDB
debugging, connecting to the terminal, etc., without letting external
agents like port scanners connect and disrupting the simulation.

Change-Id: I76dccbf152fa278ae9f342b25f7e345a1329fbe4
Reviewed-on: https://gem5-review.googlesource.com/3080
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

sockets: Add a function to disable all listening sockets.
When invoking several copies of m5 on the same machine at the same
time, there can be a race for TCP ports for the terminal connections
or remote gdb. Expose a function to disable those ports, and have the
regression scripts disable them. There are some SimObjects that have
no other function than to be used with ports (NativeTrace and
EtherTap), so they will panic if the ports are disabled.

Updated Authors from bk prs info

New directory structure:
- simulator source now in 'src' subdirectory
- imported files from 'ext' repository
- support building in arbitrary places, including
outside of the source tree. See comment at top
of SConstruct file for more details.
Regression tests are temporarily disabled; that
syetem needs more extensive revisions.

SConstruct:
Update for new directory structure.
Modify to support build trees that are not subdirectories
of the source tree. See comment at top of file for
more details.
Regression tests are temporarily disabled.
src/arch/SConscript:
src/arch/isa_parser.py:
src/python/SConscript:
Update for new directory structure.