i2c: Don't advertise i2c functions when not available
i2c: Don't advertise i2c functions when not available

Surround i2c function declarations with ifdefs, so that they aren't
advertised when i2c-core isn't actually built. That way, drivers using
these functions unconditionally will result in an immediate build
failure, rather than a late linking failure which is harder to figure
out.

Signed-off-by: Jean Delvare <49ad6a9f5aa17024c23048df346d55bda6837e01@linux-fr.org>
Cc: Mark Brown <b51b9a92386687a9ac927cebfa0f978adeb8cea5@opensource.wolfsonmicro.com>
Cc: Paul Mundt <38b52dbb5f0b63d149982b6c5de788ec93a89032@linux-sh.org>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs