[PEI] Simplify handling of targets with no phys regs. NFC
[PEI] Simplify handling of targets with no phys regs. NFC

Make doSpillCalleeSavedRegs a member function, instead of passing most of the
members of PEI as arguments.

Differential Review: https://reviews.llvm.org/D35642

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@317309 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm