rdn2cfg1/run_model.sh: Override default value for hnf_mpam_idr register

Non-secure MPAM register 'hnf_mpam_idr' on read returns 0x1007F as the
default value. However, OS expects the value to be 0x4301007F where
'0x43' indicates support for hnf_mpam_has_ccap_part and
hnf_mpam_has_cpor_part. Add additional model parameter for RD-N2-Cfg1
reference design platform to append `0x43` to the default value
returned.

Signed-off-by: Rohit Mathew <rohit.mathew@arm.com>
Change-Id: I059c58736091134206c737e9864d0f901e9dd0fb