nvic: set pending status for not active interrupts

According to ARM DUI 0552A 4.2.10. NVIC set pending status
also for disabled interrupts. Correct the logic for
when interrupts are marked pending both on input level
transition and when interrupts are dismissed, to match
the NVIC behaviour rather than the 11MPCore GIC.

Signed-off-by: Marcin Krzeminski <marcin.krzeminski@nokia.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>