LoongArch: Use the "jr" pseudo-instruction where applicable

mainline inclusion
from mainline-v5.19
commit 07b48069
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

--------------------------------

Some of the assembly code in the LoongArch port likely originated
from a time when the assembler did not support pseudo-instructions like
"move" or "jr", so the desugared form was used and readability suffers
(to a minor degree) as a result.

As the upstream toolchain supports these pseudo-instructions from the
beginning, migrate the existing few usages to them for better
readability.

Signed-off-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>