remoteproc: Introduce K3 system controller

K3 specific SoCs have a dedicated microcontroller for doing
resource management. Any HLOS/firmware on compute clusters should
load a firmware to this microcontroller before accessing any resource.
Adding support for loading this firmware.

After the K3 system controller got loaded with firmware and started
up it sends out a boot notification message through the secure proxy
facility using the TI SCI protocol. Intercept and receive this message
through the rproc start operation which will need to get invoked
explicitly after the firmware got loaded.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>