ARM: dts: msm: move duration property to flash LED node

Move duration property support to flash LED node. Moving this
property is to allow camera software get flash LED duration
information, to support flash bracketing for camera sensor

CRs Fixed: 864915
Change-Id: I71f9f5a5868e4825ebcb511438ae7266b9f0b8de
Signed-off-by: Jigarkumar Kishorkumar Zala <j_zala@codeaurora.org>