LoongArch: Add support for kernel relocation

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



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This config allows to compile kernel as PIE and to relocate it at any
virtual address at runtime: this paves the way to KASLR.

Runtime relocation is possible since relocation metadata are embedded
into the kernel.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Xi Ruoyao <xry111@xry111.site> # Use arch_initcall
Signed-off-by: Jinyang He <hejinyang@loongson.cn> # Provide la_abs relocation code
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Change-Id: I0b6310cdc4e0b93b6a02691bae36e347f8109df3