platform: mellanox: mlx-platform: Modify power off callback

Extend platform power off callback with kernel_halt() call.

When powering off, the process involves setting a halt bit in the
register space, which is then activated after a certain delay and
power off auxiliary power. By invoking `kernel_halt()` within this
timeframe, the intention is to facilitate a clean system power-off
sequence.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Michael Shych <michaelsh@nvidia.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230822113451.13785-8-vadimp@nvidia.com


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