i2c: iop3xx: use standard gpiolib functions

Instead of using the custom iop3xx gpio functions, use the gpiolib
variants. This should be functionally the same since the gpiolib
just calls the iop3xx gpio functions. This is needed in preparation
of removing iop3xx mach/io.h headers.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: "Jean Delvare (PC drivers, core)" <khali@linux-fr.org>
Cc: "Ben Dooks (embedded platforms)" <ben-linux@fluff.org>
Cc: "Wolfram Sang (embedded platforms)" <w.sang@pengutronix.de>
Cc: linux-i2c@vger.kernel.org