greybus: i2s: Remove deprecated I2S Bridged-PHY Protocol

The Greybus I2S Bridged-PHY Protocol is deprecated so remove
all support for it from the Greybus code.

CC: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Signed-off-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>