greybus: firmware: Fetch es2 VID/PID to distinguish module vendors

The es2 chip doesn't have VID/PID programmed into the hardware and we
need to hack that up to distinguish different modules and their firmware
packages.

This fetches VID/PID (over firmware protocol) for es2 chip only, when
VID/PID already sent during hotplug are 0.

Since only the bootrom contains a firmware protocol cport, this only
affects bootrom's working and not nuttx.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>