powerpc: Remove unused symbols from fsl_devices.h

Remove old artifacts leftover from the platform driver gianfar and
fsl_i2c drivers.  These symbols became unused when the drivers
were migrated over to use the of_platform bus.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>