voxel: Enable AP-driven alt mode entry
voxel: Enable AP-driven alt mode entry

Wait for the AP to direct the EC to enter USB PD alternate modes.

BUG=b:150611251,b:181144682
TEST=make buildall; observe alt mode entry
BRANCH=firmware-volteer-13672.B-main

Signed-off-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>
Change-Id: I832f69b6ed58d3502b9f6be054f295a95f94f62b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2727838
Tested-by: Prashant Malani <50de4bccb2902bfab6d92422f06eff0e3bf14c7b@chromium.org>
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>

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