[MLIR][SPIRVToLLVM] Conversion for bitrverse and bitcount ops

Implemented conversion for `spv.BitReverse` and `spv.BitCount`. Since ODS
generates builders in a different way for LLVM dialect intrinsics, I
added attributes to build method in `DirectConversionPattern` class. The
tests for these ops are in `bitwise-ops-to-llvm.mlir`.

Differential Revision: https://reviews.llvm.org/D82286