servo_v4: Advertise multiple >5V PDOs to DUT
servo_v4: Advertise multiple >5V PDOs to DUT

Select optimal PDOs from the charger at various discrete voltage limits
and advertise them all to the DUT, in case the DUT does not support the
"best" > 5V PDO due to voltage limits.

BUG=chromium:776809
BRANCH=servo
TEST=On {samus, scarlet, kevin}, with zinger attached to DUT port,
verify DUT + CHG negotiate to max supported voltage. On 'black' servo_v4
board, verify scarlet negotiates to 12V.

Change-Id: Iea174e4f6bc303d561e28281b9ff20afb3073c25
Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/730877
Commit-Ready: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Tested-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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