i965: Set MaxIfDepth to UINT_MAX on Gen6+ and 16 on prior generations.

Commit 488fe51cf8 converted the EmitNoIfs
flag to MaxIfDepth, an unsigned integer saying "flatten if-statements
nested beyond this depth."

Unfortunately, i965 left this initialized to 0, which made ir_to_mesa
attempt to flatten all if-statements.  We didn't notice right away
because we usually throw away ir_to_mesa's code in favor of the native
VS and FS backends...but this still creates a lot of unnecessary work.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_context.c

@@ -116,6 +116,7 @@ brwCreateContext(int api,
 
    /* We want the GLSL compiler to emit code that uses condition codes */
    for (i = 0; i <= MESA_SHADER_FRAGMENT; i++) {
+      ctx->ShaderCompilerOptions[i].MaxIfDepth = intel->gen < 6 ? 16 : UINT_MAX;
       ctx->ShaderCompilerOptions[i].EmitCondCodes = true;
       ctx->ShaderCompilerOptions[i].EmitNVTempInitialization = true;
       ctx->ShaderCompilerOptions[i].EmitNoNoise = true;