drivers: i2c: add system call handlers

i2c actually only has two entry points into the driver,
i2c_configure and i2c_transfer. All the other APIs are derived
from these.

All derived APIs now just call i2c_transfer() with appropriate args.

The handler for i2c_transfer() needs to examine the message array
and validate all the buffers involved depending on whether we are
reading or writing to them.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>