ACPICA: Export acpi_tb_validate_rsdp().

This patch exports acpi_tb_validate_rsdp(), so that code duplication in
some ACPICA utilities can be reduced.
This patch also includes lint changes.

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>