No intrinsic for xxspltib

[openpower-gitea-migrator]

Originally Gitea issue #76 by @toshywoshy on 2021-09-08

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We added vec_splati for xxspltiw and vec_splatid for xxspltid for P10, but didn't notice at the time that the existing xxspltib has no associated intrinsic. Should fix that in the future.