drm/amd/display: add an ASSERT() to irq service functions

Currently, if we encounter unimplemented functions, it is difficult to
tell what caused them just by looking at dmesg and that is compounded by
the fact that it is often hard to reproduce said issues, for instance we
have had reports of this condition being triggered when removing a
secondary display that is setup in mirror mode and is connected using
usb-c. So, to have access to more detailed debugging information, add an
ASSERT() to dal_irq_service_ack() and dal_irq_service_set() that only
triggers when we encounter an unimplemented function.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>