LoongArch: Use la.pcrel instead of la.abs when it's trivially possible

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



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Let's start to kill la.abs in preparation for the subsequent support of
the PIE kernel.

BTW, Re-tab the indention in arch/loongarch/kernel/entry.S for alignment.

Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Change-Id: Ia36815100690c2272528843870fa626221a5640f