i965: Allow OPCODE_SWZ to put immediates in the first arg.

Fixes assertion failure with texture swizzling in the GLSL path when
it's triggered (such as gen6 FF or ARB_fp shadow comparisons).

Fixes:
texdepth
texSwizzle
fp1-DST test
fp1-LIT test 3

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

@@ -83,6 +83,7 @@ brw_wm_arg_can_be_immediate(enum prog_opcode opcode, int arg)
       [OPCODE_SLE] = 2,
       [OPCODE_SLT] = 2,
       [OPCODE_SNE] = 2,
+      [OPCODE_SWZ] = 1,
       [OPCODE_XPD] = 2,
    };