Some operators do not work on the ARM Cortex-M backend

Several operators are currently not functioning or not fully supported on the ARM Cortex-M backend. Below is a categorization of the issues observed:

Operators not fully supported:

• Div
• Reshape
• Sigmoid
• BatchNorm

Operators without any jinja implementation:

• MatMul
• Softmax

Operators requiring correction:

• Atan