acpi: Use AcpiGbl_FACS even on ACPI_REDUCED_HARDWARE

This has been possible since ACPICA 20240827, and is actually
a requirement to get out of S3 on ACPI_REDUCED_HARDWARE (that said, we
don't implement S3 on arm64 yet).

Relevant ACPICA commit:
https://github.com/acpica/acpica/commit/79cd933e7b370e8d3fb490bf36ca5d111a12f96a.

Reviewed by:    obiwac
MFC after:      2 weeks
MFC to:         stable/15
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D54625

sys/dev/acpica/acpi.c

@@ -672,11 +672,9 @@ acpi_attach(device_t dev)
     if (AcpiGbl_FADT.Flags & ACPI_FADT_RESET_REGISTER)
 	sc->acpi_handle_reboot = 1;
 
-#if !ACPI_REDUCED_HARDWARE
     /* Only enable S4BIOS by default if the FACS says it is available. */
     if (AcpiGbl_FACS != NULL && AcpiGbl_FACS->Flags & ACPI_FACS_S4_BIOS_PRESENT)
 	sc->acpi_s4bios = 1;
-#endif
 
     /*
      * Probe all supported ACPI sleep states.  Awake (S0) is always supported,