remoteproc: qcom_q6v5_mss: Extract mba/mpss from memory-region

In the absence of mba and mpss sub-child extract the mba/mpss regions
from the memory-region property.

Tested-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Link: https://lore.kernel.org/r/20200421143228.8981-5-sibis@codeaurora.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>