ARM: dts: msm: add PON regulator support to flash LED for PMI8950/37

Add a power source, in order to support PON regulator for
torch/switch node. Torch/Switch node can enable PON regulator
when torch is in use and disable it when torch disablement
is called, in order to notify PON regulator to set/deset
spare bits to prevent from blinking when torch is in suspend.

CRs-Fixed: 997270
Change-Id: I282e0553d954e60d18a1707e7257f9930c3d355d
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>