sparc: need to reset alignment padding on SubSP/AddSP
sparc: need to reset alignment padding on SubSP/AddSP

After a SubSP the top end of the stack is used and not just unused
alignment padding anymore.

MatzeB/libfirm,libfirm/libfirm,libfirm/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,libfirm/libfirm,libfirm/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm