LoongArch: kdump: Add single kernel image implementation

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I736HO



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This feature depends on the kernel being relocatable.

Enable using single kernel image for kdump, and then no longer need to
build two kernels (production kernel and capture kernel share a single
kernel image).

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Change-Id: I28a3f91cef4ea9e54eacb573754f0c16ec744bf6