LoongArch: Add la_abs macro implementation

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



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Use the "la_abs macro" instead of the "la.abs pseudo instruction" to
prepare for the subsequent PIE kernel. When PIE is not enabled, la_abs
is equivalent to la.abs.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Change-Id: I640026372b7fe03af662aa7fa980427ab860fe5c