soc: qcom: secure_buffer: Add support for qcom,vmid-cp-camera-preview-ro

Add support for the qcom,vmid-cp-camera-preview-ro. This property
ensures that buffers for VMID_CP_CAMERA_PREVIEW are mapped with
read-only access.

Change-Id: I484e4c48965d5920e395de7958ae8c102947722d
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>