drm: add generic ioctls to get/set properties on any object

Useless for connector properties (since they already have their own
ioctls), but useful when we add properties to CRTCs, planes and other
objects.

Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Rob Clark <rob.clark@linaro.org>
Tested-by: Rob Clark <rob.clark@linaro.org>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>