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: Switch to using predefined messages for utils.

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

Change-Id: I932b7206fc16181d01a0d5b7441ce617b30e5365
Reviewed-on: https://gem5-review.googlesource.com/c/13328
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Ensure SC_LONG_64 is defined and available.

The datatype code was checking if SC_LONG_64 was defined to determine
if a long was 64 bits. The code that would define that value was
dropped when porting over from the Accellera implementation, and so
the wrong code was being included. This change both makes those checks
look at the *value* of SC_LONG_64 to ensure that it's not missing by
accident, and assigns it a value in sc_fxdefs.hh.

Change-Id: Ie9bb1146452a3db1d9d99c0db575098bb06463ff
Reviewed-on: https://gem5-review.googlesource.com/c/12616
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add the Accellera implementation for the data type classes.

These files have been cleaned up style wise, and some macros have been
resolved like they were for the header files.

Change-Id: I447e5311961036847e7da0c5a86c0da25a633010
Reviewed-on: https://gem5-review.googlesource.com/10844
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>