fix poweroff regression from 9cdf326b4f by delaying shutdown_halt

The regression affected ACPI-based systems without EFI poweroff support
(including VMs).

The key reason for the regression is that I overlooked that poweroff is
requested by RB_POWEROFF | RB_HALT combination of flags. In my opinion,
that command is a bit bipolar, but since we've been doing that forever,
then so be it. Because of that flag combination, the order of
shutdown_final handlers that check for either flag does matter.

Some additional complexity comes from platform-specific shutdown_final
handlers that aim to handle multiple reboot options at once. E.g.,
acpi_shutdown_final handles both poweroff and reboot / reset. As
explained in 9cdf326b4f, such a handler must run after shutdown_panic to
give it a chance. But as the change revealed, the handler must also run
before shutdown_halt, so that the system can actually power off before
entering the halt limbo.

Previously, shutdown_panic and shutdown_halt had the same priority which
appears to be incompatible with handlers that can do both poweroff and
reset.

The above also applies to power cycle handlers.

PR: 276784
Reported by: many
Tested by: Katsuyuki Miyoshi <katsubsd@gmail.com>,

		Masachika ISHIZUKA <ish@amail.plala.or.jp>

Fixes: 9cdf326b4fae run acpi_shutdown_final later to give other handlers a chance
MFC after: 1 week