get_sp() only worked by accident, because gcc inlined calls
to it. It should have always been explicitly inlined. It was
also only added for debugging, and not in any use now.
Furthermore, while we will have need for a "get_sp", we'll
add it back with a new name, current_stack_pointer, in order
to be consistent with Linux.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>