fixes for QEMU 9.0

fixes for QEMU 9.0

Most importantly, fix forwards and backwards migration with VirtIO-GPU
display.

Other fixes are for a regression in pflash device (introduced in 8.2)
and some fixes for x86(_64) TCG emulation. One of the patches needed
to be adapted, because it removed a helper that is still in use in
9.0.0.

There also is a revert for a fix in VirtIO PCI devices that turned out
to cause some issues, see the revert itself for more details.

Lastly, there is a change to move compatibility flags for a new
VirtIO-net feature to the correct machine type. The feature was
introduced in QEMU 8.2, but the compatibility flags got added to
machine version 8.0 instead of 8.1. This breaks backwards migration
with machine version 8.1 from a 8.2/9.0 binary to an 8.1 binary, in
cases where the guest kernel enables the feature (e.g. Ubuntu 23.10).
While that breaks migration with machine version 8.1 from an unpatched
to a patched binary, Proxmox VE only ever had 8.2 on the test
repository and 9.0 not yet in any public repository. An upstream
developer suggested it is the proper fix [0]. Upstream submission [1].

[0]: https://lore.kernel.org/qemu-devel/CACGkMEtZrJuhof+hUGVRvLLQE+8nQE5XmSHpT0NAQ1EpnqfmsA@mail.gmail.com/T/#u
[1]: https://lore.kernel.org/qemu-devel/20240517075336.104091-1-f.ebner@proxmox.com/T/#u

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>