ARM: dts: msm-pmi8994: add LED:SWITCH node to combine both flashLED channel

Add LED:SWITCH node to combine both flashLED channel. Also, move
duration properties from individual to common node property.

Change-Id: Icf74ae3be6100cc32c9af272d76371679da6c640
Signed-off-by: Jigarkumar Kishorkumar Zala <j_zala@codeaurora.org>