[RFC PATCH] pwm: add pwm-atmel from Linux kernel 4.14

[Sam Ravnborg]

Hi Sascha.

> > While working with this I get the impression that the core
> > should know about pwm channels and device_d pointer
> > should be part of the core data.
> 
> I know it's done like this in Linux. Any good reason to do this in
> barebox aswell besides of "do it as in Linux"?

The overall structure is something like this:

  PWM Controller       PWM Channel
  +------------+
  |            |     +------------+
  |  pwm_chip  |====>| pwm_device |+
  |            |     +------------+|
  +------------+      +------------+

And with the current core support each implementation
needs to provide their owm implementation of this.
And I can see the core has data I think belongs
on another level.

So having better core support should simplify the individual
implementations a bit - I think.

When I get pwm-atmel working I may try to give it a shot.
If things turns out positivie I will post patches.

	Sam