systemc: Switch to using predefined messages for datatypes.

Create and use predefined messages for datatypes which match the ones
Accellera uses.

Change-Id: I92dd52f62462b864264217bb81f3ff1dcec020bf
Reviewed-on: https://gem5-review.googlesource.com/c/13331
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: "Fix" some error message formatting.

These changes make the output match what Accellera outputs so that the
tests will pass.

Change-Id: I1260cec35fa39586fbef39047b9da4ff3c03b3ed
Reviewed-on: https://gem5-review.googlesource.com/c/12592
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Fix a typo/bug in sc_int_base.hh.

When being turned into gem5 coding style, a pair of "!" operators were
dropped, reversing the behavior of the functions involved.

Change-Id: Ife795c22aff953c5ab592e7baa3a5e1c15e63c84
Reviewed-on: https://gem5-review.googlesource.com/c/12591
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

Systemc: Port over all of the systemc "datatype" headers.

These are the headers originally written by Accellera with a few
modifications. Most significantly, I went through and mostly (but not
entirely) manually editted them to conform to gem5 style and to be
more self consistent. Second, I resolved some macros which optionally
select features. I removed support for deprecated functions, and
otherwise enabled everything.

The actual implementation behind these headers will also be ported
over, but in a subsequent change.

Change-Id: I203d3f6c8a3af9120b946001d01defbb0643a6b6
Reviewed-on: https://gem5-review.googlesource.com/10843
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add systemc and systemc.h header files.

These are the header files as defined by the standard, although some
predefined channel types and most of the sc_dt namespace have yet to be
stubbed out, and so those portions are excluded.

Change-Id: Ic70f887c06e591974a4265c820eb0fdfa740d19a
Reviewed-on: https://gem5-review.googlesource.com/10838
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Seperate the "external" header interface.

Most (but not all) of the SystemC headers are part of the "external"
interface that an existing, standard compliant module would include
through <systemc.h> or <systemc>. Since those follow slightly different
rules (relative includes, no gem5 includes), this change separates them
out so that they're easier to identify.

Also, this change moves the other files into a "core" subdirectory,
with the intention to add a "dt", aka data type, directory some time in
the future when those standard defined types are implemented.

Change-Id: Ida63f9cc0bc0431024d4dd691cc5b22b944a99a8
Reviewed-on: https://gem5-review.googlesource.com/10835
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>