llvm: add SPIRV-LLVM-Translator support

llvm: add SPIRV-LLVM-Translator support

Mesa builds require SPIRV-LLVM-Translator in order to build CLC support.
While it is possible to build it separately (like meta-clang does), it
also requires a separate clang compiler (which OE-Core doesn't provide).

Use an alternative path and build SPIRV-LLVM-Translator as a part of the
LLVM build process, lifting the requirement for the separate clang. Once
Clang is properly integrated into the OE-Core layer, this can be split
to a separate package and dropped. In order to ease migration from
meta-clang and to ease future split, PROVIDE the spirv-llvm-translator
and make the llvm-spirv package RPROVIDE spirv-llvm-translator.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>