Allow x86 subtargets to use the GenericModel defined in X86Schedule.td.
Allow x86 subtargets to use the GenericModel defined in X86Schedule.td.

This allows codegen passes to query properties like
InstrItins->SchedModel->IssueWidth. It also ensure's that
computeOperandLatency returns the X86 defaults for loads and "high
latency ops". This should have no significant impact on existing
schedulers because X86 defaults happen to be the same as global
defaults.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@161370 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,chubbymaggie/asap,dslab-epfl/asap,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,chubbymaggie/asap,dslab-epfl/asap,dslab-epfl/asap,GPUOpen-Drivers/llvm,chubbymaggie/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,chubbymaggie/asap,chubbymaggie/asap,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,dslab-epfl/asap,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,chubbymaggie/asap,apple/swift-llvm,llvm-mirror/llvm