TCPMv2: Discover cable plug modes
TCPMv2: Discover cable plug modes

Enter PE_INIT_VDM_Modes_Request with transmit type SOP', following
cable-plug (SOP') SVID discovery.

BUG=b:152420269,b:152419795
TEST=Attach port partner via cable; TCPM sends SOP' modes request and
TEST=then continues with mode entry.
BRANCH=none

Change-Id: I62be147e7809ee3955c1db7704e965f576176f67
Signed-off-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2174468
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