i965: enable ARB_shader_precision in gen7+
i965: enable ARB_shader_precision in gen7+

Reviewed-by: Andreas Boll <041cac00e0cb793452cecf5c52a77db13d069cf3@gmail.com>
Reviewed-by: Francisco Jerez <5906ff32bdd9fd8db196f6ba5ad3afd6f9257ea5@riseup.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler