arm: dts: msm: specify the type of strobe for flash led

Add a device tree parameter to specify if the strobe type for flash
led is software. The strobe type is hardware by default.

Change-Id: I6480b6ae79a07b1f56dfa3d54b45fa061b3ab30a
Signed-off-by: Abinaya P <abinayap@codeaurora.org>