ARM: dts: msm: add dummy ibb regulator supply for amoled panel

When the AMOLED panel is powered from the external power source,
the IBB regulator is not needed. In the absence of ibb regulator
node we are getting error message (non-fatal) for AMOLED panel's
operation on ibb during change in the power states. Using stub
regulator for ibb supply to fix this error.

Change-Id: Id11164a846e0034801980b3e1417cf47ad996e70