Fix build breakage introduced in commit "[POWERPC] i2c: OF helpers for
the i2c API".  If i2c-core is compiled as a module, the helper needs
to be compiled as a module, as well.  Rename i2c.c to of_i2c.c to
avoid name space conflict.

[paulus@samba.org: Changed dependency from OF to PPC_OF to avoid
sparc{32,64} allmodconfig breakage.]
Signed-off-by: NJochen Friedrich <jochen@scram.de>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

This implements various helpers to support OF bindings for the i2c
API.
Signed-off-by: NJochen Friedrich <jochen@scram.de>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NPaul Mackerras <paulus@samba.org>