0 isn't a valid rotation property value, so let's set the initial value
of the property to DRM_ROTATE_0 instead.

In the same vein, we must always have at leat one angle as part of set
of supported rotation bits, so let's include DRM_ROTATE_0 in there.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Jilai Wang <jilaiw@codeaurora.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>