remoteproc: k3-r5: Acquire mailbox handle during probe routine

remoteproc: k3-r5: Acquire mailbox handle during probe routine

Acquire the mailbox handle during device probe and do not release handle
in stop/detach routine or error paths. This removes the redundant
requests for mbox handle later during rproc start/attach. This also
allows to defer remoteproc driver's probe if mailbox is not probed yet.

Signed-off-by: Beleswar Padhi <b-padhi@ti.com>
Link: https://lore.kernel.org/r/20240808074127.2688131-3-b-padhi@ti.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>