platform/rd: adapt to changes in cmn model parameters

The location of the RNSAM (internal or externa) can be specified using
model parameters. Due to changes in the names of the model parameters
used to specify the location of the RNSAM, adapt the model launch
scripts for the same.

Change-Id: Ia2f61b4d17264df0a2ab9149d2ca998b51521c7b
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>