greybus: es1,es2: add USB vendor command to timestamp

As part of an effort to get deep inspection of latencies throughout the
greybus network including HSIC, UniPro and firmware incurred latencies a
new command to the APBridge to tag a known offset with timestamping data
has been introduced. This patch adds that code to the es1 and es2 drivers.

- latency_tag_enable
- latency_tag_disable

Respectively send the enable/disable command to APBridge on a per-CPort
basis. This allows only specified cports to have timestamping data added by
APBridge, leaving any CPort not specifically enabled untouched.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>