sparc: Harden signal return frame checks.

sparc: Harden signal return frame checks.

    Orabug: 23303740

    [ Upstream commit d11c2a0de2824395656cf8ed15811580c9dd38aa ]

    All signal frames must be at least 16-byte aligned, because that is
    the alignment we explicitly create when we build signal return stack
    frames.

    All stack pointers must be at least 8-byte aligned.

    Signed-off-by: David S. Miller <davem@davemloft.net>
    Conflicts:

    arch/sparc/kernel/signal32.c - modified patch context so that it would apply

    Signed-off-by: Larry Bassel <larry.bassel@oracle.com>
    Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>