[TTI] NFC: Change getCFInstrCost to return InstructionCost

This patch migrates the TTI cost interfaces to return an InstructionCost.

See this patch for the introduction of the type: https://reviews.llvm.org/D91174
See this thread for context: http://lists.llvm.org/pipermail/llvm-dev/2020-November/146408.html

Reviewed By: samparker

Differential Revision: https://reviews.llvm.org/D100313

GitOrigin-RevId: 14b934f8a6f2aeade5a512c5004ec88837f363f5
15 files changed