i2c: ocores: Move grlib set/get functions into #ifdef CONFIG_OF block

This moves the grlib set and get functions into the #ifdef CONFIG_OF block to
avoid warnings of unimplemented functions when compiling with -Wunused-function
when CONFIG_OF is not defined.

Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>