iommu/arm-smmu-v3: remove unnecessary mpam enable procedure

ascend inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4LMGH


CVE: NA

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When mpam feature is not supported in IDR3_MPAM register, there's
no need to enable it because the register can not be modified. So
remove the enable procedure and unnecessary warning message.

Signed-off-by: Xingang Wang <wangxingang5@huawei.com>
Reviewed-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>