[BOLT][BAT] Fix handling of split functions

Move BAT parent function lookup outside `getLocationName`, to the
scope where we retrieve `FuncBranchData` linked with the function.

Previously DataAggregator would store branch profile recorded in the
split fragment in `FuncBranchData` associated with the fragment, and
perform name translation in `getLocationName` for symbol name only.
This works for fdata profile which is printed out as-is, but doesn't
work with BAT YAML profile writer which requires a combined profile.

The issue necessitated `fixupBATProfile` which partially addressed the
issue (reassigned inter-fragment calls back into intra-function
branches). However, `fixupBATProfile` fails to address disjoint
profiles (i.e. doesn't merge `FuncBranchData` for fragments back
into parent). This diff eliminates the need for `fixupBATProfile` by
removing the root cause of the issue.

Test Plan: NFC for existing tests

Reviewers: ayermolo, dcci, rafaelauler, maksfb

Reviewed By: maksfb

Pull Request: https://github.com/llvm/llvm-project/pull/87569