ec/google/wilco: Always use current value of battery status bit

According to the Wilco EC spec the BTSC bit of PWSR is always cleared
when PWSR is read so that battery status change events are only
triggered one time. Testing of the Wilco EC has verified this behavior.
This changes the way in which the battery status change bit is used from
checking the bit state against the previous value to always issuing a
battery event when the BTSC bit is set. The other bits in PWSR indicate
state directly and do not behave like the BTSC bit.

BUG=b:157113138
TEST=Deploy on Drallion and verify that battery events are generated
BRANCH=drallion, sarien

Signed-off-by: Mathew King <mathewk@chromium.org>
Change-Id: I8fbf2ee1158ddd790b04a20b1eb27a6cce4f5c81
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42017
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

src/ec/google/wilco/acpi/event.asl

@@ -25,7 +25,11 @@ Method (ECQP, 0, Serialized)
 		}
 	}
 
-	If (EBIT (BTSC, Local1)) {
+	/*
+	 * Battery status is cleared when read so always use the value from
+	 * PWSR directly regardless of the previous value stored in ECPR.
+	 */
+	If (EBIT (BTSC, Local0)) {
 		Printf ("BAT0 Status Change")
 		Notify (BAT0, 0x80)
 	}