drm/amd/display: log destination of vertical interrupt

[Why]
Knowing the destination of OTG's vertical interrupt 2 is useful for
debugging, but it is not currently included in the OTG state readback
logic

[How]
Read the OTG interrupt destination register to get the vertical interrupt
2 destination on ASICs that have this register when reading back the OTG
state from hardware

Reviewed-by: Sung Lee <sung.lee@amd.com>
Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Josip Pavic <Josip.Pavic@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>