i965: Add LINTERP/CINTERP to can_do_cmod().

LINTERP is implemented as a PLN instruction or a LINE+MAC. PLN and MAC
can do conditional mod. CINTERP is just a MOV.

total instructions in shared programs: 5952103 -> 5950284 (-0.03%)
instructions in affected programs:     324573 -> 322754 (-0.56%)
helped:                                1819

We lose the SIMD16 in one Unigine Heaven shader which appears six times
in shader-db.

src/mesa/drivers/dri/i965/brw_shader.cpp

@@ -905,6 +905,8 @@ backend_instruction::can_do_cmod() const
    case BRW_OPCODE_SHR:
    case BRW_OPCODE_SUBB:
    case BRW_OPCODE_XOR:
+   case FS_OPCODE_CINTERP:
+   case FS_OPCODE_LINTERP:
       return true;
    default:
       return false;