drm/amd/display: Create underflow interrupt IRQ type

[WHY]
We want another entry in IRQ type that can be used to
help find the underflow interrupt source.

[HOW]
Added another mapping in IRQ type enum.
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Angus Wang <Angus.Wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/irq_types.h

@@ -162,6 +162,7 @@ enum irq_type
 	IRQ_TYPE_VUPDATE = DC_IRQ_SOURCE_VUPDATE1,
 	IRQ_TYPE_VBLANK = DC_IRQ_SOURCE_VBLANK1,
 	IRQ_TYPE_VLINE0 = DC_IRQ_SOURCE_DC1_VLINE0,
+	IRQ_TYPE_DCUNDERFLOW = DC_IRQ_SOURCE_DC1UNDERFLOW,
 };
 
 #define DAL_VALID_IRQ_SRC_NUM(src) \