ACPICA: iASL: Add support for to_PLD macro.

This macro is intended to simplify the constuction of _PLD buffers.
NOTE: Prototype only, subject to change before this macro is
added to the ACPI specification. David E. Box.

Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>