pwm: add pwm-mxs support

Add generic PWM framework driver (DT only) for Freescale MXS.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>

diff --cc Documentation/devicetree/bindings/pwm/mxs-pwm.txt
Simple merge

diff --cc drivers/pwm/Kconfig
Simple merge

diff --cc drivers/pwm/Makefile
Simple merge

diff --cc drivers/pwm/pwm-mxs.c
Simple merge