dde_linux: improve handling of interrupt masking and acknowledgement

[chelmuth]

While debugging pc_nic_drv link handling, I discovered that unmasked pending interrupts are sometimes not delivered immediately. This was caused by sloppy task execution that is fixed by 1ea641a paired with shaky handling of interrupt masking and acknowledgement. I addressed the latter in a work-in-progress commit on x86/pc, but then discovered that ARM comes with a slightly different implementation of irqchip.c regarding EOI and ACK.

May we merge the both implementations?

If not, could someone check if arm/irqchip.c contradicts my work in progress?

[chelmuth]

Commit fb00f4a reflects my WIP.

[skalk]

I would very much appreciate, if we can merge both irqchip variants (x86, arm). They are in my eyes not so much architecture dependent, it's more a question of configuration. The arm variant reflects the different needs already a bit by the CONFIG_IRQ_DOMAIN_HIERARCHY optional part. If we put several parts into a CONFIG_OF optional part too, we would gain an almost identical version.
The EOI when doing unmask in the arm version might be located there for no particular reason. The development history was such that x86 came later, and EOI got placed differently. I would think we can check whether it works in the ARM case the same way.
Another function provided in the arm case is .irq_set_wake, which seems to have no value regarding functionality, I think we can simply remove it. The function .irq_set_type (only in arm) might be necessary, but probably it does not disturb the x86 scenarios.