The interrupts are not stable while uses guest physical address (GPA)
for interrupt packet write space even on direct loading case.

v2: make condition more readable
Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>