acpi: 'hw.acpi.s4bios' sysctl: Change type to bool, expand description

Another boolean, indicating hardware support, will be introduced in next commit.

Thanks to the previous commit modifying sysctl_handle_bool(), this
change is backwards-compatible with old programs using an integer in and
out of sysctl(3).

Reviewed by:    obiwac
MFC after:      2 weeks
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D54626

sys/dev/acpica/acpi.c

@@ -626,7 +626,7 @@ acpi_attach(device_t dev)
 
     /* 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;
+	sc->acpi_s4bios = true;
 
     /*
      * Probe all supported ACPI sleep states.  Awake (S0) is always supported,
@@ -754,9 +754,9 @@ acpi_attach(device_t dev)
     SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
 	OID_AUTO, "sleep_delay", CTLFLAG_RW, &sc->acpi_sleep_delay, 0,
 	"sleep delay in seconds");
-    SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
+    SYSCTL_ADD_BOOL(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
 	OID_AUTO, "s4bios", CTLFLAG_RW, &sc->acpi_s4bios, 0,
-	"Use S4BIOS when hibernating.");
+	"On hibernate, have the firmware save/restore the machine state (S4BIOS).");
     SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
 	OID_AUTO, "verbose", CTLFLAG_RW, &sc->acpi_verbose, 0, "verbose mode");
     SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),

sys/dev/acpica/acpivar.h

@@ -64,7 +64,7 @@ struct acpi_softc {
     enum power_stype	acpi_lid_switch_stype;
 
     int			acpi_standby_sx;
-    int			acpi_s4bios;
+    bool		acpi_s4bios;
 
     int			acpi_sleep_delay;
     int			acpi_do_disable;