acpi_wmi: Allow attachment to ACPI node if EC is not found.

[wulf]

Summary

Some tests with Acer ACPI extras on my Aspire S7 laptop shows that at least ome WMI extensions do not depend on EC, so we can exclude this strict dependency like Linux does.

This reduces amount of console spam on EC-less devices like "Gigabyte X299X AORUS MASTER desktop motherboard" where acpi_wmi.ko is autoloaded by devmatch.

[wulf]

Committed as bde56c994264.

Thank you, @avg