TCPMv2: PE: Don't set AMS flag unless custom VDM has a reply
TCPMv2: PE: Don't set AMS flag unless custom VDM has a reply

This CL fixes an issue related to PE_FLAGS_INTERRUPTIBLE_AMS which was
being set in pe_handle_custom_vdm_request_entry whether the custom VDM
request is supported or not. This would result in
PE_FLAGS_INTERRUPTIBLE_AMS remaining set and ignoring of subsequent VDM
messages, which in turn prevents ALT-DP entry for UFP case.

BUG=b:189293176
BRANCH=quiche
TEST=Verfied that with this fix, ALT-DP mode is entered
consistently. Without this CL, ALT-DP mode is not entered correctly.

Signed-off-by: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@google.com>
Change-Id: I7a52a6028ea656d9a1970fea0b42f582f1aaff5c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2677707
Commit-Queue: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>
Tested-by: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

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