sparc: more platform headers

Previous commit adding these was merged very quickly, so here's one
more...

Change-Id: I23c424db7631db1f0ec48e2d0ae47c8409ae6af2
Reviewed-on: https://review.haiku-os.org/c/1088
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

sparc: add defines and minimum set of required files

Gets the stage0 bootstrap to run.
Imlementation is probably nonsense at this point.

Change-Id: I10876efbb54314b864c0ad951152757cdb2fd366
Reviewed-on: https://review.haiku-os.org/c/1061
Reviewed-by: waddlesplash <waddlesplash@gmail.com>