r: add Piezo support (led_pwm) on PWM4 as /sys/class/leds/buzzer

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Merge branch 'boundary-imx_3.0.35_4.1.0' of github.com:boundarydevices/linux-imx6 into boundary-imx_3.0.35_4.1.0