mb/google/brya/acpi: Don't clear GC6 flag after GC6 entry

According to Nvidia, the GC6 flag (DFEN) should not get cleared after
a successful GC6 entry; the kernel driver will not re-inform ACPI
that the exit should be GC6 exit as well.

BUG=b:243888246
BRANCH=brya
TEST=tested by Nvidia

Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Change-Id: I220795928d03f269de48278ea0ab57de7253fad5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67745
Reviewed-by: Tarun Tuli <taruntuli@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/brya/acpi/power.asl

@@ -338,6 +338,7 @@ Method (NPON, 0, Serialized)
 /* Handle deferred GC6 vs. poweroff request */
 Method (NPOF, 0, Serialized)
 {
+	/* Don't touch the `DFEN` flag until the GC6 exit. */
 	If (DFEN == GC6_DEFER_ENABLE)
 	{
 		/* Deferred GC6 entry */
@@ -345,8 +346,6 @@ Method (NPOF, 0, Serialized)
 		{
 			GC6I ()
 		}
-
-		DFEN = GC6_DEFER_DISABLE
 	}
 	Else
 	{