power: reset: Add QEMU virt-ctrl driver

Add a new driver for the 'virt-ctrl' device found on QEMU virt machines
(e.g. m68k). This device provides a simple interface for system reset
and power off [1].

This driver utilizes the modern system-off API to register callbacks
for both system restart and power off. It also registers a reboot
notifier to catch SYS_HALT events, ensuring that LINUX_REBOOT_CMD_HALT
is properly handled. It is designed to be generic and can be reused by
other architectures utilizing this QEMU device.

Link: https://gitlab.com/qemu-project/qemu/-/blob/v10.2.0/hw/misc/virt_ctrl.c [1]
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://patch.msgid.link/20260222173225.1105572-2-visitorckw@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>