USB-PD: Disable Vconn on SRC_DISCONNECT
USB-PD: Disable Vconn on SRC_DISCONNECT

Currently, source only devices do not turn off Vconn when a partner
is disconnected. This causes the polarity detection to be disabled.

This patch turns off Vconn on SRC_DISCONNECT for
!CONFIG_USB_PD_DUAL_ROLE boards.

Signed-off-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

BUG=b/122861749
BRANCH=Kalista
TEST=Plug in an ethernet dongle via a USB-C-to-A adapter. Replug it
upside down and verify Ethernet is turned on on both sides.

Change-Id: I4ac303f2121d9e4114ce7097db304e4f65f27ae0
Reviewed-on: https://chromium-review.googlesource.com/1412228
Commit-Ready: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Tested-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Reviewed-by: Zhuohao Lee <916bf7ddbf0565669e59e3cb2b613381a48066c0@chromium.org>

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