drm/amd/display: Flatten irq handler data struct

[Why]
There is no reason why the common data needs to be kept separate.

[How]
Flatten the struct by moving common data into the DM IRQ struct.

Signed-off-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>