platform: implement K210 system reset

Implement rebooting the K210 via the system reset extension.

All reset types are treated in the same way.
A request for shutdown results in a reboot.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>