soc/intel/common/acpi: correct return value for PEPD enum function

The PEPD enum function returns a bitmask to announce supported/enabled
PEPD functions. Add a comment describing this bitmask and correct the
return value to announce function 1, 5 and 6 as supported.

Also add comments to the disabled functions 3 and 4.

Change-Id: Ib523a54f5ad695e79005aba422282e03f2bc4bed
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>

src/soc/intel/common/block/acpi/acpi/pep.asl

@@ -26,7 +26,12 @@ Device(PEPD)
 			 * Enum functions
 			 */
 			If(Arg2 == PEPD_DSM_LPI_ENUM_FUNCTIONS) {
-				Return(Buffer(One) {0x60})
+				/*
+				 * Supported functions bitmask
+				 * bit 0:    other functions than 0 are supported
+				 * bits 1-6: function x supported
+				 */
+				Return(Buffer(1) {0x63})
 			}
 			/*
 			 * Function 1 - Get Device Constraints
@@ -56,16 +61,19 @@ Device(PEPD)
 			 * Function 2 - Get Crash Dump Device
 			 */
 			If(Arg2 == PEPD_DSM_LPI_GET_CRASH_DUMP_DEV) {
+				/* not yet used and not advertised by function 0 */
 			}
 			/*
 			 * Function 3 - Display Off Notification
 			 */
 			If(Arg2 == PEPD_DSM_LPI_DISPLAY_OFF_NOTIFY) {
+				/* not yet used and not advertised by function 0 */
 			}
 			/*
 			 * Function 4 - Display On Notification
 			 */
 			If(Arg2 == PEPD_DSM_LPI_DISPLAY_ON_NOTIFY) {
+				/* not yet used and not advertised by function 0 */
 			}
 			/*
 			 * Function 5 - Low Power S0 Entry Notification