ARM: dts: msm: add PMIC revid source property for flash LED

Add PMIC revid source property, in order to differentiate
between PMIC subtypes and revisions for flash LED.
Since MSM8937 device uses both the PMICs i.e. PMI8937 and
PMI8950, thus add the change in both PMI DTSI.

Change-Id: Id9f8b9372e424257745fe69f8aa735370cb51430
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>