ACPI: Set hotplug _OST support bit to _OSC

When ACPI_HOTPLUG_OST is defined, set hotplug _OST support bit
OSC_SB_HOTPLUG_OST_SUPPORT to indicate that the OS supports hotplug
_OST by calling the platform-wide ACPI Operating System Capabilities
(_OSC).

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>