drm/amd/display: Add dc_ctx to link_enc_create() parameters

[Why&How]
Preparation to enable run time initialization of register offsets to add
dc_context to the link_enc_create callback. This is needed to get the
dc_ctx handle where register offset initialization routine is called.

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>