w83627hf: add method to retrieve wake event source register to ASL include

Add a method WAKS to devtree.asl which returns the wake-up source register
to simplify retrieving the wake source e.g. in \_WAK.

Change-Id: Ia258f8fc9ff79b18391c55464da73863889e2255
Signed-off-by: Christoph Grenz <christophg+cb@grenz-bonn.de>
Reviewed-on: http://review.coreboot.org/297
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/superio/winbond/w83627hf/devtree.asl

@@ -1503,5 +1503,22 @@ Scope (\_SB)
 			}
 		}
 		#endif
+
+		/* Returns the wake source register.
+		   It is cleared after reading.
+		   Bit 0: Keyboard wake-up event
+		   Bit 1: Mouse wake-up event
+		   Bit 2: Power button event
+		   Bit 3: CIR wake-up event
+		   Bit 4: Power loss event
+		   Bit 5: VSB power loss status
+		*/
+		Method (WAKS) {
+			ENCM ()
+			Store (0x0A, LDN)
+			Store (CRE3, Local0)
+			EXCM ()
+			Return (Local0)
+		}
 	}
 }