sw64: extend pt_regs to fix broken bpf_user_pt_regs_t

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I73KLE



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Make struct user_pt_regs prefix of struct pt_regs like other
architectures.

Fix the compile error introduced in the previous commit.

This patch will increase overhead of SAVE_ALL and RESTORE_ALL.

Signed-off-by: Mao Minkai <maominkai@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>