dt-bindings: msm: Add strings for secondary panel ctrl, phy and clocks

This change adds panel device tree strings for DSI Controller,
PHY and Clocks for secondary panel.

Change-Id: I5b009c298efbe850a9e4f0945eb4d637174814b2
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>