genirq/msi: Provide default .irq_eoi() for MSI chips

Currently only platform-MSI irqchips get a default .irq_eoi() when
MSI_FLAG_USE_DEF_CHIP_OPS is set. There's no reason PCI-MSI irqchips
couldn't benefit from this too, so let all MSI irqchips benefit from this
default.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>