Commit 40d225009ef accidentally changed the behaviour of
gic_acknowledge_irq() for the NVIC. The NVIC doesn't have SGIs,
so this meant we hit an assertion:
gic_acknowledge_irq: Assertion `s->sgi_pending[irq][cpu] != 0' failed.
Return NVIC acknowledge-irq to its previous behaviour, like 11MPCore.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>