userswap: split uswap_register() to validate address ranges

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6CAIM



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Split uswap_register() into uswap_register() and uswap_adjust_uffd_range().
Before validate_range(), use uswap_register() to handle uswap mode.
After validate_range(), use uswap_adjust_uffd_range() to change address
range to VMA range, which could reduce fragmentation caused by VMA
splitting.
By splitting uswap_register(), we could prevent the userswap registration
of invalid input address ranges.

Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>