LoongArch: Add signal handling support

mainline inclusion
from mainline-v5.19-rc1
commit b74baf4a
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

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Add ucontext/sigcontext definition and signal handling support for
LoongArch.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>