compat: backport __i2c_transfer()

compat: backport __i2c_transfer()

mcgrof@frijol ~/linux-stable (git::master)$ git describe --contains b37d2a3a
v3.6-rc1~28^2~265

commit b37d2a3a75cb0e72e18c29336cb2095b63dabfc8
Author: Jean Delvare <khali@linux-fr.org>
Date:   Fri Jun 29 07:47:19 2012 -0300

    [media] i2c: Export an unlocked flavor of i2c_transfer

    Some drivers (in particular for TV cards) need exclusive access to
    their I2C buses for specific operations. Export an unlocked flavor
    of i2c_transfer to give them full control.

    The unlocked flavor has the following limitations:
    * Obviously, caller must hold the i2c adapter lock.
    * No debug messages are logged. We don't want to log messages while
      holding a rt_mutex.
    * No check is done on the existence of adap->algo->master_xfer. It
      is thus the caller's responsibility to ensure that the function is
      OK to call.

    Signed-off-by: Jean Delvare <khali@linux-fr.org>
    Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>