ACPICA: Update RSDP table definitions.

This patch updates RSDP table header definitions as such enhancement
has been made in ACPICA upstream already.  It ports that change to
the Linux source to reduce source code differences between Linux and
ACPICA upstream.

This patch does not affect the generation of the Linux kernel binary.

[rjw: Changelog]
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>