greybus: gbphy: Remove protocol specific version handling

We should be using the generic version handling at bundle level, instead
of at protocol level for bridged PHY devices as well.

The bundle version handling is already in place, though it is *not* used
today as we haven't bumped the version of control protocol yet.

Remove protocol specific handling for bridged PHY devices.

Tested on EVT 1.5 with gpbridge-test module. No nuttx changes are
required with this.

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>