gnome-keyring: add (from oe-core)

This was previously in oe-core but nothing there was actually using it in an
image.  As it's part of GNOME, move it meta-gnome.

The custom service file is dropped, as upstream is now shipping and installing
this file (and has been for some time).

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>