ACPICA: Add helper macros to extract bus/segment numbers from HEST table.

This change adds two macros to extract the encoded bus and segment
numbers from the HEST Bus field.

Signed-off-by: Betty Dall <betty.dall@hp.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>