arm/dt: 8974: Fix IOMMU context bank interrupts

The IOMMU driver expects context fault interrupts to go to
the non-secure IOMMU interrupt. MSM8974-sim is the only
target not following this pattern.

Change-Id: I17101246672c8bc7d5efbdf8d465e751c2134dbc
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>