acpi_wmi noisy without EC

[Yuri Pankov]

I have started seeing the following on boot since some time:

acpi_wmi0: <ACPI-WMI mapping> on acpi0
acpi_wmi0: cannot find EC device
device_attach: acpi_wmi0 attach returned 6
acpi_wmi0: <ACPI-WMI mapping> on acpi0
acpi_wmi0: cannot find EC device
device_attach: acpi_wmi0 attach returned 6
acpi_wmi0: <ACPI-WMI mapping> on acpi0
acpi_wmi0: cannot find EC device
device_attach: acpi_wmi0 attach returned 6
acpi_wmi0: <ACPI-WMI mapping> on acpi0
acpi_wmi0: cannot find EC device
device_attach: acpi_wmi0 attach returned 6

Likely following this commit:

commit 708d048ccfdacf6199cc08a56aa05a9c899441fd
Author: Vladimir Kondratyev <wulf at FreeBSD.org>
Date:   Sat Oct 31 22:19:39 2020 +0000

    acpi_wmi(4): Add ACPI_PNP_INFO

While the reason is obvious -- there's no EC in this system (Gigabyte X299X AORUS MASTER desktop motherboard), at least searching the `acpidump -dt` output doesn't show any PNP0C09 entries -- it certainly looks like "something is broken" when first noticed.  I wonder if we could/should handle this gracefully -- no EC, do nothing, simply exit?