dt-bindings: remoteproc: qcom,pas: Add iommus property

On most Qualcomm platforms, the Qualcomm Hypervisor Execution
Environment (QHEE) is either used as a standalone hypervisor or
co-exists as a module with the Gunyah hypervisor. When QHEE is
present, it configures firmware streams for remote processors.
If QHEE is not available, the operating system must perform
these configurations instead and for that remote processor
firmware stream should be presented to the operating system.
To support this, add the iommus property as an optional property
for PAS-supported devices.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Mukesh Ojha <mukesh.ojha@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260105-kvmrprocv10-v10-1-022e96815380@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>