remoteproc: qcom_q6v5_pas: add support for assigning memory to firmware

Starting with SM8550, the DSM memory must now be shared to the
firmware by the APPS process instead of beeing defined in the
carveout memory reserved for MPSS.

In order to handle that, add a region_assign_idx in adsp_data
to specify with index of memory-region must be assigned to
the MPSS via the qcom_scm_assign_mem() call at probe time.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>