pwm: Move TWL6030 PWM driver to PWM framework

This commit moves the driver to drivers/pwm and converts it to the new
PWM framework. In order for this to work properly, register the PWM as
child of the multi-function TWL6030 device.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>