Disable stack overflow check for MPU ports (#1231)

Disable stack overflow check for MPU ports (#1231)

Disable stack overflow check for MPU ports

Stack overflow check is not straight forward to implement for MPU ports
because of the following reasons:
1. The context is stroed in TCB and as a result, pxTopOfStack member
   points to the context location in TCB.
2. System calls are executed on a separate privileged only stack.

It is still okay because an MPU region is used to protect task stack
which means task stack overflow will trigger an MPU fault.

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>