gpio: Add basic support for TWL6040 GPOs

TWL6040 provides GPO lines to be used for controlling external devices.The number
of lines different between versions: twl6040 have 3 GPO while TWL6041 have 1.

Signed-off-by: Sergio Aguirre <saaguirre@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>