hw/intc/arm_gicv3_its: Pass DTEntry to update_dte()

Make update_dte() take a DTEntry struct rather than all the fields of
the new DTE as separate arguments.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220201193207.2771604-4-peter.maydell@linaro.org