[SYCL] Add sycl-enable-bfloat16-conversion compilation flag#4343

MrSidims wants to merge 4 commits intointel:syclintel/llvm:syclfrom

MrSidims:private/MrSidims/BF16OptionMrSidims/llvm:private/MrSidims/BF16OptionCopy head branch name to clipboard