mm/sharepool: Don't check the DVPP address space range before merging

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5DS9S


CVE: NA

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The user doesn't care about the start address of the dvpp range, what
is mattered is that the virtual space tagged DVPP located at in a 16G
range. So we can safely drop the dvpp address space as long as it's
empty during merging process.

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>