mfd: Detach twl6040 from the pmic mfd driver

On OMAP4 platform audio has separate IC, it is no longer part
of the pmic chip.
Prevent twl-core to claim the 0x4b address, which belongs to
the twl6040 audio IC.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>