ARM: dts: msm: Add led blinking support for dtp8996

The RGB leds which are connected on PMI device is able to support blinking
by configuring the PWM channel. The property 'qcom,use-blink' will add
blink sysfs to allow the userspace code to control the blinking behavior.

CRs-Fixed: 936764
Change-Id: Ieab34a932be17eff17f360cad94b7bed989b7701
Signed-off-by: Chunmei Cai <ccai@codeaurora.org>