PEI: Delay checking requiresFrameIndexReplacementScavenging

PEI: Delay checking requiresFrameIndexReplacementScavenging

Currently this is called before the frame size is set on the
function. For AMDGPU, the scavenger is used for large frames where
part of the offset needs to be materialized in a register, so
estimating the frame size is useful for knowing whether the scavenger
is useful.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357087 91177308-0d34-0410-b5e6-96231b3b80d8