drm/amd/display: Make dcn401_program_pipe non static

Allow reuse of code by making dcn401_program_pipe()
non static.

Fixes: 2739bd12 ("drm/amd/display: Allow reuse of of DCN4x code")
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Karthi Kandasamy <karthi.kandasamy@amd.com>
Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>