style: [patch 1/22] use /r/3648/ to reorganize includes

ruby: update WireBuffer API to match that of MessageBuffer

this patch updates the WireBuffer API to mirror the changes in revision 11111

ruby: rename System.{hh,cc} to RubySystem.{hh,cc}

The eventual aim of this change is to pass RubySystem pointers through to
objects generated from the SLICC protocol code.

Because some of these objects need to dereference their RubySystem pointers,
they need access to the System.hh header file.

In src/mem/ruby/SConscript, the MakeInclude function creates single-line header
files in the build directory that do nothing except include the corresponding
header file from the source tree.

However, SLICC also generates a list of header files from its symbol table, and
writes it to mem/protocol/Types.hh in the build directory. This code assumes
that the header file name is the same as the class name.

The end result of this is the many of the generated slicc files try to include
RubySystem.hh, when the file they really need is System.hh. The path of least
resistence is just to rename System.hh to RubySystem.hh.

ruby: replace global g_system_ptr with per-object pointers

This is another step in the process of removing global variables
from Ruby to enable multiple RubySystem instances in a single simulation.

With possibly multiple RubySystem objects, we can no longer use a global
variable to find "the" RubySystem object. Instead, each Ruby component
has to carry a pointer to the RubySystem object to which it belongs.

ruby: remove message buffer node

This structure's only purpose was to provide a comparison function for
ordering messages in the MessageBuffer. The comparison function is now
being moved to the Message class itself. So we no longer require this
structure.

ruby: move files from ruby/system to ruby/structures

The directory ruby/system is crowded and unorganized. Hence, the files the
hold actual physical structures, are being moved to the directory
ruby/structures. This includes Cache Memory, Directory Memory,
Memory Controller, Wire Buffer, TBE Table, Perfect Cache Memory, Timer Table,
Bank Array.

The directory ruby/systems has the glue code that holds these structures
together.