drm/amd/display: Check if link state is valid

[ Upstream commit 03ce7b38 ]

The link state is set to false if there is no link and local sink. Even
though the stream state may not change, it is desirable to commit the
new stream when HPD goes low to high.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Co-developed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: 59de751e ("drm/amd/display: add ODM case when looking for first split pipe")
Signed-off-by: Sasha Levin <sashal@kernel.org>