LoongArch: Consolidate __ex_table construction

mainline inclusion
from mainline-v6.2-rc1
commit 508f28c6
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6BWFP


CVE: NA

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Consolidate all the __ex_table constuction code with a _ASM_EXTABLE or
_asm_extable helper.

There should be no functional change as a result of this patch.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Change-Id: I24db0d24f7ec183f687221f9d99c4eb8f17cebd2
(cherry picked from commit da2cf6dc)