hw/intc/arm_gicv3_its: Range-check ICID before indexing into collection table

hw/intc/arm_gicv3_its: Range-check ICID before indexing into collection table

In process_its_cmd(), we read an ICID out of the interrupt table
entry, and then use it as an index into the collection table.  Add a
check that it is within range for the collection table first.

This check is not strictly necessary, because:
 * we range check the ICID from the guest before writing it into
   the interrupt table entry, so the the only way to get an
   out of range ICID in process_its_cmd() is if a badly-behaved
   guest is writing directly to the interrupt table memory
 * the collection table is in guest memory, so QEMU won't fall
   over if we read off the end of it

However, it seems clearer to include the check.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20220111171048.3545974-14-peter.maydell@linaro.org