MLBEDSW-5209 Vela: output diff depthwise with non-zero zero points

Fixed by adjusting zero points for ops with int8 IFM and asymmetric weights
since the reference does not support asymmetric weights for int8 IFM and
ignores the zero points.

Signed-off-by: Fredrik Svedberg <fredrik.svedberg@arm.com>
Change-Id: I2a206a01a471a53aa864a6a3616aa23d2a5a23c8
diff --git a/ethosu/vela/tensor.py b/ethosu/vela/tensor.py
index d62ebc8..8c5e277 100644
--- a/ethosu/vela/tensor.py
+++ b/ethosu/vela/tensor.py
@@ -209,7 +209,17 @@
 
 
 class QuantizationParameters:
-    __slots__ = "min", "max", "num_bits", "narrow_range", "scale_f32", "zero_point", "quant_min", "quant_max"
+    __slots__ = (
+        "min",
+        "max",
+        "num_bits",
+        "narrow_range",
+        "scale_f32",
+        "zero_point",
+        "quant_min",
+        "quant_max",
+        "quant_dim",
+    )
 
     def __init__(
         self,
@@ -228,6 +238,7 @@
         self.zero_point: Union[int, np.ndarray, None] = None
         self.quant_min: Optional[float] = None
         self.quant_max: Optional[float] = None
+        self.quant_dim: Optional[int] = None
 
     def __str__(self):
         return "<nng.QuantizationParameters min=%s max=%s, num_bits=%s, scale=%s, zero_point=%s>" % (
@@ -252,6 +263,7 @@
         res.zero_point = self.zero_point
         res.quant_min = self.quant_min
         res.quant_max = self.quant_max
+        res.quant_dim = self.quant_dim
         return res
 
     def dequantize(self, values) -> np.ndarray: