ub: ubcore add import/unimport seg api.

driver inclusion
category: feature
bugzilla: NA
CVE: NA

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

Ubcore add import/unimport seg api, which will finally call hw driver's
registered method import/unimport seg.

import_seg:
The UB Core invokes the UBN driver to import segments and keys.
Input parameter:
dev: UB device to which the remote segment is imported.
cfg: specifies the basic information about the remote segment to be
imported by the ubcore protocol stack.
udata: contains the pointer of the URMA context and the address of the
private data exchanged between the UBN user-mode driver and kernel-mode
driver.
Output parameter:
None.
Return value:
If the import is successful, the target segment structure pointer
is returned. The returned information includes the segment address and
length. The import fails and NULL is returned.

unimport_seg:
The UB Core invokes the UBN driver to unimport the remote segment and key.
Input parameter:
tseg: pointer to the target segment
Return value:
The value 0 indicates that the unimport is successful.
Other values indicate that the unimport fails.

Signed-off-by: Guoxin Qian <qianguoxin@huawei.com>
Signed-off-by: Yizhen Fan <fanyizhen@huawei.com>