RDMA/hns: Refactor hns_roce_alloc_ucontext()

driver inclusion
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I87LTM



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In the hns_roce_alloc_ucontext() function, the configuration
code is too much. Extract this part of the code into the function
hns_roce_get_uctx_config() to improve readability.

Signed-off-by: Juan Zhou <zhoujuan51@h-partners.com>