ARM: dts: omap3-beagle-xm: Use pwm-leds for pmu_stat LED

We have proper driver stack to handle the pmu_stat LED which is connected
PWMB of twl4030.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>