chip/mt_scp: change uart clock to ULPOSC
chip/mt_scp: change uart clock to ULPOSC

Change UART clock to ULPOSC to keep SCP console alive when system
suspend.

BRANCH=none
BUG=b:189300514
TEST=make BOARD=cherry_scp

Change-Id: I144354fe946808c7ec68da4ea33e4ad11a7bf11f
Signed-off-by: Tinghan Shen <c9ff063c8de5b2a8e3ffacf80169ee51e722b470@mediatek.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3003345
Tested-by: Tzung-Bi Shih <5e6f7578cd434ae5b4c9ffe5250f7a87a25045d7@chromium.org>
Reviewed-by: Tzung-Bi Shih <5e6f7578cd434ae5b4c9ffe5250f7a87a25045d7@chromium.org>
Commit-Queue: Tzung-Bi Shih <5e6f7578cd434ae5b4c9ffe5250f7a87a25045d7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec