cassini-bsp: Disable virtualization warning for Corstone-1000 FW

The layer config for meta-virtualization prints a warning when the layer
is included but virtualization features are not enabled. Virtualization
features are not used when building the Corstone-1000 firmware with
multiconfig so the warning is shown.

Skip the sanity check that prints this warning for the Corstone-1000
firmware build.

Signed-off-by: Adam Johnston <adam.johnston@arm.com>