radeonsi: add support for easy opcodes from ARB_gpu_shader5
radeonsi: add support for easy opcodes from ARB_gpu_shader5

I have to use the BFE instrinsics, because BFE is one of the most complex
instructions that can't be matched easily. BFE has 3 conditional branches
and one of them is quite big.

In the isel DAG, lowered BFE has 27 nodes (including leafs).

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler