chip/mt_scp: mt8195 uses 32k clock when AP suspend

Use 32k clock instead of ULPOSC can significantly reduce the power
consumption of SCP under S3 stage, and still able to kick SCP WDT.

BRANCH=none
BUG=b:197937562
TEST=low scp power in S3 stage

Change-Id: If2f68a5b11e93c7e6badf2e4893f649700b5af2e
Signed-off-by: Tinghan Shen <[email protected]>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3131409
Reviewed-by: Tzung-Bi Shih <[email protected]>
Commit-Queue: Tzung-Bi Shih <[email protected]>

Author: tinghan-shen

chip/mt_scp/mt8195/clock.c

@@ -377,7 +377,7 @@ power_chipset_handle_host_sleep_event(enum host_sleep_event state,
 {
 	if (state == HOST_SLEEP_EVENT_S3_SUSPEND) {
 		CPRINTS("AP suspend");
-		clock_select_clock(SCP_CLK_ULPOSC2_LOW_SPEED);
+		clock_select_clock(SCP_CLK_32K);
 	} else if (state == HOST_SLEEP_EVENT_S3_RESUME) {
 		CPRINTS("AP resume");
 		clock_select_clock(SCP_CLK_ULPOSC2_HIGH_SPEED);