ACPICA: Update buffer-to-string conversions

Add "0x" prefix for hex values.
Provides compatibility with other ACPI implementations.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>