svm: add support for allocing memory which is within 4G physical address in svm_mmap

ascend inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4JMM0


CVE: NA

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Add alloc and release memory functions in svm. And the physical address
of the memory is within 4GB.

For example:
    /* alloc */
    fd = open("dev/svm0",);
    mmap(0, ALLOC_SIZE,, MAP_PA32BIT, fd, 0);

    /* free */
    ioctl(fd, SVM_IOCTL_RELEASE_PHYS32,);
    close(fd);

Signed-off-by: Lijun Fang <fanglijun3@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>