acpi: Use sleep types defined in sys/power.h

This is as opposed to using ACPI sleep states (ACPI_STATE_S*). We now
use POWER_STYPE_* added in D52036.

This is in preparation for adding support for s2idle, which is not an
ACPI sleep state, but needs to be handled specially by
acpi_EnterSleepState.

Supersedes D48732.

Reviewed by: mckusick (mentor), markj
Approved by: mckusick (mentor), markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52043