PPC: Clean up DECR implementation

There are 3 different variants of the decrementor for BookE and BookS.

The BookE variant sets TSR[DIS] to 1 when the DEC value becomes 1 or 0. TSR[DIS]
is then the indicator whether the decrementor interrupt line is asserted or not.

The old BookS variant treats DEC as an edge interrupt that gets triggered when
the DEC value's top bit turns 1 from 0.

The new BookS variant maintains the assertion bit inside DEC itself. Whenever
the DEC value becomes negative (top bit set) the DEC interrupt line is asserted.

So far we implemented mostly the old BookS variant. Let's do them all properly.

This fixes booting pseries ppc64 guest images in TCG mode for me.

Signed-off-by: Alexander Graf <agraf@suse.de>

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v1 -> v2:

  - Use timer callback to trigger IRQ, it gets overridden by e500
PPC: Only enter MSR_POW when no interrupts pending

We were entering the power saving state even when interrupts (like an
external interrupt or a decrementer interrupt) were still in flight.

In case we find a pending interrupt, don't enter power saving state.

Signed-off-by: Alexander Graf <agraf@suse.de>
ppce500_spin: Initialize struct properly

The spinning struct is in guest endianness, so we need to initialize
its variables in guest endianness too.

This fixes booting e500 guests with SMP on x86 for me.

Signed-off-by: Alexander Graf <agraf@suse.de>