This patch adds framework support for PWM (pulse width modulation)
devices.
A new pwm can be registered from a hardware driver using
pwmchip_add(). It can then be requested from a client driver using
pwm_request(). A string is used as a unique identifier for the
pwms. It should usually be initialized by the hardware drivers
using dev_name(dev). The client API is the same as currently
in the Linux Kernel.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>