disp: msm: dsi: set source to xo while turning off PLL

HW recommendation is to park the DSI byte clock and pixel clock at XO
before turning them off. The change parses XO from the DT and sets the
clock source as XO while turning off the PLL.

Change-Id: I788951d6341149300e80e8db4a5a3fd2c4eb3e03
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>

msm/dsi/dsi_ctrl.h

@@ -119,6 +119,7 @@ struct dsi_ctrl_power_info {
  *			output of the PLL is set as parent for these root
  *			clocks. These clocks are specific to controller
  *			instance.
+ * @xo_clk:             XO clocks used to park the DSI PLL before turning off.
  * @mux_clks:           Mux clocks used for Dynamic refresh feature.
  * @ext_clks:           External byte/pixel clocks from the MMSS block. These
  *			clocks are set as parent to rcg clocks.
@@ -131,6 +132,7 @@ struct dsi_ctrl_clk_info {
 	struct dsi_link_hs_clk_info hs_link_clks;
 	struct dsi_link_lp_clk_info lp_link_clks;
 	struct dsi_clk_link_set rcg_clks;
+	struct dsi_clk_link_set xo_clk;
 
 	/* Clocks set by DSI Manager */
 	struct dsi_clk_link_set mux_clks;