mm: Ignore madvise(MADV_MERGEABLE) request for VM_CDM marked VMAs

ascend inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4JMLR


CVE: NA
-------------------

VMA containing CDM memory should be excluded from KSM merging. This change
makes madvise(MADV_MERGEABLE) request on target VMA to be ignored.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Lijun Fang <fanglijun3@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>