Because Hyper-V requires that hypercall arguments be aligned on an 8
byte boundary, add __aligned(8) to struct retarget_msi_interrupt.

Link: https://lore.kernel.org/lkml/87k1hlqlby.fsf@vitty.brq.redhat.com/Signed-off-by: NMaya Nakamura <m.maya.nakamura@gmail.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>