sparc: implement thread local storage support

The sparc ABI reserves the g7 register for this.

Change-Id: I93b81ecef72cde859972ef7b7f6b9991d35f9f29
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3583
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>