flash_ec: Have iteflash use I2C through servod with CR50 CCD.
flash_ec: Have iteflash use I2C through servod with CR50 CCD.

Previously flash_ec would instruct iteflash to communicate directly with
CR50 when using CCD.  Now the same communication path through servod is
used with Servo Micro is also used with CR50.

Benefits:

1) Allows for resolving b:126189871 without adding significant new
   complexity in servod.

   Without this, fixing that bug would involve implementing
   CR50 I2C USB endpoint disconnect and reconnect commands, exposing them
   through dut-control, and ensuring they play nicely with
   I2cPseudoAdapter.

   With this, that bug can be trivially fixed, and then the retry loop in
   flash_ec around dut_i2c_mux:ec_prog can be deleted.

2) Simplifies flash_ec with slightly less differences needed in iteflash
   invocation.

BRANCH=none
BUG=b:75976718,b:79684405,b:124388894,b:126189871
CQ-DEPEND=CL:1250029,CL:1546592
TEST=The following servo + board combinations were tested:
flash_ec -> iteflash -> servo_micro -> bip
flash_ec -> iteflash -> servo_v4 -> servo_micro -> bip
flash_ec -> iteflash -> servo_v2 -> bip
flash_ec -> iteflash -> servo_v4 -> cr50 -> bip

Change-Id: I36009b01e45576c786ea78853baf46b52d2232d6
Signed-off-by: Matthew Blecker <d18f4466f2802f9c78c5c14a42b8c21fdbfabfcd@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1522846
Reviewed-by: Namyoon Woo <e8732cefb861f07768f47df788a8e8eb75efc09a@chromium.org>

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