mm/sharepool: Add an interface to obtain an id

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5EORS


CVE: NA

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

The DVPP address space is per process or per sharing group.
During sp_free and unshare, you need to know which address
space the current address belongs to.

Signed-off-by: Zhou Guanghui <zhouguanghui1@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>