drm: Move property validation to a helper, v2.

Property lifetimes are equal to the device lifetime, so the separate
drm_property_find is not needed. The pointer can be retrieved from
the properties member, which saves us some locking and a extra lookup.
The lifetime for properties is until the device is destroyed, which
happens late in the device unload path.

kms_atomic is also testing for invalid properties which returns -ENOENT,
to be consistent return -ENOENT for valid properties that don't appear
on the object property list.

Changes since v1:
- Return -ENOENT for invalid properties to make kms_atomic pass.
- Change commit message slightly to take this into account.

Testcase: kms_atomic
Testcase: kms_properties
Fixes: 4e9951d96093 ("drm/atomic: Reject properties not part of the object.")
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/599c7fa8-b6fd-a42b-c619-a9e4a9c5c244@linux.intel.com