acpi.4: Update sysctl descriptions for new stypes

The previous S1-S5 options are still accepted for compatibility, but
they are now deprecated in favour of the new generic sleep types.

Reported by: markj
Reviewed by: markj
Approved by: markj
Fixes: 97d152698f48 ("acpi: Use sleep types defined in sys/power.h")
Event: AsiaBSDCon 2026
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D56008