acpi_ged: New driver to ACPI generic event device

New driver to ACPI generic event device, defined in ACPI spec.
Some ACPI power button may not work without this.

In qemu arm64 with "virt" machine, with ACPI firmware,
enable devd check devd message by
and invoke following command in qemu monitor
(qemu) system_powerdown
and make sure some power button input event appear.
(setting sysctl hw.acpi.power_button_state=S5 is not work,
because ACPI tree does not have \_S5 object.)

Reviewed by: andrew, hrs
Differential Revision: https://reviews.freebsd.org/D37032
(cherry-picked from a9880bfe1181b7a32d026339bae113f24300e5e1)

acpi_ged: fix build, as module and non INTRNG case.

Reviewed-by: cy

Differential Revision: https://reviews.freebsd.org/D37104
(cherry-picked from 9cf5db63698b3c73edd632412bf68735d3c20d37)
acpi_ged: fix build with ACPI_DEBUG
(cherry-picked from ba23f762ece54a86f64b8ef62bbfc9c73c98762c)

Make it compile for 13-stable.