platform/x86: mlx-platform: Configure notifier callbacks for modular system

Add event notifier callbacks for modular system line cards. These
callbacks are to be passed to "mlxreg-hotplug" driver by line card
driver during probing. Then, when any line card related hotplug event
is received (insertion ,power, synch, ready), hotplug driver will
invoke callback for the relevant line card.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Michael Shych <michaelsh@nvidia.com>
Link: https://lore.kernel.org/r/20211002093238.3771419-5-vadimp@nvidia.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>