m68k: virt: Switch to qemu-virt-ctrl driver

Register the "qemu-virt-ctrl" platform device during board
initialization to utilize the new generic power/reset driver.

Consequently, remove the legacy reset and power-off implementations
specific to the virt machine. The platform's mach_reset callback is
updated to call do_kernel_restart(), bridging the legacy m68k reboot
path to the generic kernel restart handler framework for this machine.

To prevent any regressions in reboot or power-off functionality when
the driver is not built-in, explicitly select POWER_RESET and
POWER_RESET_QEMU_VIRT_CTRL for the VIRT machine in Kconfig.machine.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://patch.msgid.link/20260222173225.1105572-3-visitorckw@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>