LoongArch: Add build infrastructure

mainline inclusion
from mainline-v5.19-rc1
commit fa96b57c
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

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Add Kbuild, Makefile, Kconfig and link script for LoongArch build
infrastructure.

Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>