remoteproc: xlnx: Add shutdown callback

In case of kexec call, each driver's shutdown callback is called. Handle
this call for rproc driver and shutdown/detach each core that was powered
on before. This is needed for proper Life Cycle Management of remote
processor. Otherwise on next linux boot, remote processor can't be
started due to bad refcount of power-domain managed by platform
management controller.

Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
Link: https://lore.kernel.org/r/20250620195728.3216935-1-tanmay.shah@amd.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>