Revert "drm: Unify handling of blob and object properties"

This reverts commit 77953bd1.

This causes a kernel panic when trying to assign a blob to a property,
and has obviously never been tested.

Fixes: 77953bd1 ("drm: Unify handling of blob and object properties")
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Tested-by: Liu Ying <gnuiyl@gmail.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/8c0d3482-1bb5-6a15-b105-6bda2b31b5dc@linux.intel.com