ASoC: audio-graph-card: Drop remote-endpoint as required property

The remote-endpoint may not be available if it is part of some
pluggable module. One such example would be an audio card, the
Codec endpoint will not be available until it is plugged in.
Hence drop 'remote-endpoint' as a required property.

Cc: Rob Herring <robh@kernel.org>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Sameer Pujar <spujar@nvidia.com>
Link: https://lore.kernel.org/r/1610948585-16286-1-git-send-email-spujar@nvidia.com


Signed-off-by: Mark Brown <broonie@kernel.org>