Use const pointers in APIs where appropriate

[newling]

In an iree project we are using functions like XAie_DmaGetMaxQueueSize in a C++ class for modeling AIE devices. The class stores a XAie_DevInst * as a class member which is used in class getter 'methods' to, for example, get the maximum queue size. The should ideally be const member functions.

As the functions in xaie_dma.h do not ever take const pointers as arguments, we have a problem: we either have to make our class getters non-const, or use a C++ const_cast under the hood before calling the aie-rt API. We don't like either of these options -- the first means we have to pass the model class by non-const reference even though it is never mutated, and the second means that we implicitly rely on aie_rt not to change the value pointed to.

So request: use const correctness where possible. I'll make a PR demonstrating this soon