sw64: vdso: fix CFI directives for fpregs in vrt_sigreturn

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I56P0Z



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SW64 uses 256-bit fpregs and has very special indexes for vector regs.
Fix CFI directives in vdso rt_sigreturn accordingly.

Signed-off-by: Mao Minkai <maominkai@wxiat.com>

Signed-off-by: Gu Zitao <guzitao@wxiat.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>