May I suggest this name is likely a hypocoristic (affectionate nickname), and as such would more frequently take the form *Bardilô?
In support of this suggestion, I would point out that it is a diminutive, and these are often used in hypocoristics. The classic example is Gothic Wulfila < *Wulfilô, both a hypocoristic and a diminutive.
Germanic names traditionally had two elements, and either of these could be chosen as the nickname, which was then declined as weak masculine (*-ô) or weak feminine (*-ǭ). The same usage applied to certain diminutives: *mawī > *mawilǭ and *maguz > *magulô.
These single-element hypocoristics then become names in their own right: Audǭ > Ute.
The other possibility for Bardilô, rather than deriving it from a two-element name with *bardaz as an element, is that the person in question had a distinctive beard.
The use of the *-ô ending as a hypocoristic is a shared feature between Germanic, Latin and Greek: Catō, Πλάτων.