ACPI : Use RSDT instead of XSDT by adding boot option of "acpi=rsdt"

On some boxes there exist both RSDT and XSDT table. But unfortunately
sometimes there exists the following error when XSDT table is used:
   a. 32/64X address mismatch
   b. The 32/64X FACS address mismatch

   In such case the boot option of "acpi=rsdt" is provided so that
RSDT is tried instead of XSDT table when the system can't work well.

http://bugzilla.kernel.org/show_bug.cgi?id=8246

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
cc:Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/kernel-parameters.txt

@@ -139,6 +139,7 @@ and is between 256 and 4096 characters. It is defined in the file
 			ht -- run only enough ACPI to enable Hyper Threading
 			strict -- Be less tolerant of platforms that are not
 				strictly ACPI specification compliant.
+			rsdt -- prefer RSDT over (default) XSDT
 
 			See also Documentation/power/pm.txt, pci=noacpi