mm/sharepool: Unify the memory allocation process

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


CVE: NA

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There are two types of memory allocated from sharepool: passthrough
memory for DVPP and shared memory. Currently, we branch to different
routines depending on the memory type, both during the allocation and
free process. Since we have already create a local group for passthrough
memory, with just one step ahead, we could drop the redundant branches
in allocation and free process and in all the fallback process when an
error occurs.

Here is the content of this patch:
1. Add erery process to its local group when initilizing its group_master.
2. Avoid to return the local group in find_sp_group_id_by_pid().
3. Delete the redundant branches during allocation and free process.

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>