sw64: rewrite elf core copy interfaces

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I56OLG



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For gpreg, simplify dump method to make it easier to maintain.

For fpreg, redefine elf_fpregset_t with struct user_fpsimd_state and
add a arch-specific dump_fpu() method.

Signed-off-by: He Sheng <hesheng@wxiat.com>

Signed-off-by: Gu Zitao <guzitao@wxiat.com>