[why]
Only a single VLINE interrupt is available so interface should not
expose the second one which is used by DMU firmware.

[how]
Remove references to periodic_interrupt1 and VLINE1 from DC interfaces.
Reviewed-by: Jaehyun Chung <jaehyun.chung@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>