Merge git://git.denx.de/u-boot-rockchip

This adds a new firefly-rk3399 board, MIPI support for rk3399 and
rk3288, rk818 pmic support, mkimage improvements for rockchip and a few
other things.

doc: dtbinding: add pwm binding file

This is a copy from kernel.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>