sparc,sparc64: prepare vmlinux.lds.S for unification

This patch makes the two vmlinux.lds.S files identical
and serve as documentation for the changes in each file.

This mainly add stuffs to sparc32 that is otherwise only
used by sparc64 and thus it should have no effect.

Build tested only.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>