If I understand the code correctly, MSI_ALLOC_FLAGS_SHARED_DEVICE is
supposed to be set in info->flags in platform_msi_set_desc(), but this
is called per-msi after its_msi_prepare(), so we don't the flags set
at the right time. That's how it looks to me...
Meh. I was trying multiple things, and of course commited the worse
possible approach.
I've updated the branch, having verified that we do get the flag in
the ITS now.