sparc: More missing defines in platform headers

* Kernel is 64 bit, and we won't need a 32bit load base.

Change-Id: I729bab01c8f71083002db061e153b0e5052b9a1c
Reviewed-on: https://review.haiku-os.org/c/1326
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

kernel: tweak USER_SIZE.

Change-Id: Id0a4ad785bbd195e425dd32ca891dc4525bb3e18
Reviewed-on: https://review.haiku-os.org/c/1151
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

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>