Add a parameter to mbedtls_hardware_poll(). And to reduce confusion it shouldn't have the same name, and so the name can be modernized (though it won't be an official PSA API). The parameters should be the same with one addition: the new function should be able to convey the entropy content of the data gathered. (The callers don't need to use this yet, this is to allow future development during 4.x.)

The description of MBEDTLS_ENTROPY_HARDWARE_ALT should spell out the function signature and shouldn't reference an internal header. (MBEDTLS_ENTROPY_HARDWARE_ALT and the corresponding function is part of the stable API, any header in which the function might appear isn't necessarily stable and we should limit the confusion by removing this link.)