drm/tegra: remove irrelevant DRM_UNLOCKED flag

DRM_UNLOCKED doesn't do anything for non-legacy drivers. Remove it.

Cc: Thierry Reding <treding@nvidia.com>
Cc: linux-tegra@vger.kernel.org
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190522154702.16269-1-emil.l.velikov@gmail.com