servo_v4: Support command to limit the max_voltage
servo_v4: Support command to limit the max_voltage

firmware_PDVbusRequest forces servo v4 to different max_voltage
limits to verify the PD negotiation. Add the firmware support for it.
The console command usbc_action is the same as Plankton. So the test
side doesn't need any change.

BRANCH=servo
BUG=b:134700685
TEST=Tried usbc_action command and ran firmware_PDVbusRequest passed.

Change-Id: I5f05d73d9a2f92fe26514285e7c251e9fa27aba8
Signed-off-by: Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1686221
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

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