ARM: dts: msm: Add sync boost support for flash LED

Flash LED requires enabling sync boost before it is used as torch
light. Previous implementation has the issue that flash LED torch
mode does not work when battery is low.

CRs-Fixed: 502393
Change-Id: Ica562ec58cf0c3afc825ec1c4bf18b8540adcc57
Signed-off-by: Chun Zhang <chunz@codeaurora.org>