The GICv3 Software Overview suggests when allocating a new MSI/MSI-X
interrupt we need to call MAPD followed by MAPTI. Unfortunately the code
would place a MOVI command between these. This is invalid as it needs
values set by the MAPTI to be present.
Re-order so we allocate a temporary CPU for the interrupt, then use the
MAPTI command to assign the MSI to it.
MFC after: 2 weeks
Sponsored by: DARPA, AFRL
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