ACPI: thinkpad-acpi: add X61t HKEY events

Tomas Carnecky reports that events 0x5009 and 0x500a are swivel events, and
that 0x500b/0x500c are tablet pen storage bay events.

Document these events, and avoid nasty messages when they happen.
Signed-off-by: NHenrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: NLen Brown <len.brown@intel.com>

Documentation/thinkpad-acpi.txt

@@ -499,6 +499,10 @@ The above events are never propagated by the driver.
 
 0x3003		Bay ejection (see 0x2x05) complete, can sleep again
 0x4003		Undocked (see 0x2x04), can sleep again
+0x5009		Tablet swivel: switched to tablet mode
+0x500A		Tablet swivel: switched to normal mode
+0x500B		Tablet pen insterted into its storage bay
+0x500C		Tablet pen removed from its storage bay
 0x5010		Brightness level changed (newer Lenovo BIOSes)
 
 The above events are propagated by the driver.

drivers/misc/thinkpad_acpi.c

@@ -2127,10 +2127,13 @@ static void hotkey_notify(struct ibm_struct *ibm, u32 event)
 			}
 			break;
 		case 5:
-			/* 0x5000-0x5FFF: On screen display helpers */
+			/* 0x5000-0x5FFF: human interface helpers */
 			switch (hkey) {
-			case 0x5010:
-				/* Lenovo Vista BIOS: brightness changed */
+			case 0x5010: /* Lenovo new BIOS: brightness changed */
+			case 0x5009: /* X61t: swivel up (tablet mode) */
+			case 0x500a: /* X61t: swivel down (normal mode) */
+			case 0x500b: /* X61t: tablet pen inserted into bay */
+			case 0x500c: /* X61t: tablet pen removed from bay */
 				break;
 			case 0x5001:
 			case 0x5002: