arm/module: Use plt section indices for relocations

hulk inclusion
category: feature
bugzilla: 51921
CVE: NA

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

We are planning to add livepatch without ftrace support for arm
in the next commit. However after commit 425595a7 ("livepatch:
reuse module loader code to write relocations") merged, the klp
relocations is done by apply_relocate function.

The mod->arch.{core,init}.plt pointers were problematic for livepatch
because they pointed within temporary section headers (provided by the
module loader via info->sechdrs) that would be freed after module load.

Here we take same modification based on commit c8ebf64e
("arm64/module: use plt section indices for relocations") to solve.

Signed-off-by: Dong Kai <dongkai11@huawei.com>

Signed-off-by: Ye Weihua <yeweihua4@huawei.com>
Reviewed-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>