[X86] Avoid uses of getZextValue(). NFCI.
[X86] Avoid uses of getZextValue(). NFCI.

Use getAPIntValue() directly - this is mainly a best practice style issue to help prevent fuzz tests blowing up when a i12345 (or whatever) is generated.

Use getConstantOperandVal/getConstantOperandAPInt wrappers where possible.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@371315 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm