greybus: gpbridge: rename 'gpbridge' to 'gbphy' everywhere
The 'gpbridge' name didn't relaly reflect what the bus is; which
is a bus for bridged-phy devices. So, rename all instances
of 'gpbridge' to more appropriate 'gbphy'
Testing Done:
Build and boot tested. 'lsgb' will stop displaying 'GPBridge' devices
until I change the library to reflect this change.