[mlir][SPIRVToLLVM] Propagate location attribute from spv.GlobalVariable to llvm.mlir.global

This patch is mainly to propogate location attribute from spv.GlobalVariable to llvm.mlir.global.

It also contains three small changes.

1. Remove the restriction on UniformConstant In SPIRVToLLVM.cpp;
2. Remove the errorCheck on relaxedPrecision when deserializering SPIR-V in Deserializer.cpp
3. In SPIRVOps.cpp, let ConstantOp take signedInteger too.

Co-authered: Alan Liu <alanliu.yf@gmail.com> and Xinyi Liu <xyliuhelen@gmail.com>

Reviewed by:antiagainst

Differential revision: https://reviews.llvm.org/D110207