remoteproc: k3-m4: Add pointer to rproc struct within k3_m4_rproc

remoteproc: k3-m4: Add pointer to rproc struct within k3_m4_rproc

Add a pointer to the rproc struct within k3_m4_rproc internal struct.
This is done to align the M4 internal rproc data structure with R5
driver which can be factored out at a later stage.

Signed-off-by: Beleswar Padhi <b-padhi@ti.com>
Tested-by: Judith Mendez <jm@ti.com>
Reviewed-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20250513054510.3439842-11-b-padhi@ti.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>