platform_data/mlxreg: Add field for notification callback

Add notification callback to inform caller that platform driver probing
has been completed. It allows to caller to perform some initialization
flow steps depending on specific driver probing completion.

Signed-off-by: Michael Shych <michaelsh@nvidia.com>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20220430115809.54565-2-michaelsh@nvidia.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>