The function has little to do with atomic, it's just where it has so
far been needed. So, rename it to drm_property_replace_blob, move it
to drm_property.c and export it.

Change the semantics to return whether the blob was replaced instead
of using an extra argument for that.
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170713162538.22788-2-peda@axentia.se