video: omap: add support for DM/DTS

Update the driver to support the device tree and the driver model.
Timings and panel parameters are now loaded from the device tree.

The DM code replaces the am335x_lcdpanel structure with
tilcdc_panel_info taken from the linux kernel, as well the management
of additional parameters not covered in the legacy code. In addition,
the am335x_lcdpanel structure contains parameters and operations that
were probably a requirement of the board for which this driver was
developed and which, however, were not developed in the linux kernel.
All this led to rewrite th DM controller initialization code, except
for the pixel clock setting that is executed in a function created in a
previous patch with code taken from the legacy am335xfb_init.

The patch has been tested on a custom board with u-boot 2018.11-rc2 and
the following device-tree configuration:

	panel {
		compatible = "ti,tilcdc,panel";
		pinctrl-names = "default";
		pinctrl-0 = <&lcd_enable_pins>;
		enable-gpios = <&gpio0 31 0>;
		backlight = <&backlight>;
		status = "okay";
		u-boot,dm-pre-reloc;
		panel-info {
			ac-bias           = <255>;
			ac-bias-intrpt    = <0>;
			dma-burst-sz      = <16>;
			bpp               = <16>;
			fdd               = <0x80>;
			sync-edge         = <0>;
			sync-ctrl         = <1>;
			raster-order      = <0>;
			fifo-th           = <0>;
		};
		display-timings {
			native-mode = <&timing0>;
			timing0: 800x480 {
				hactive         = <800>;
				vactive         = <480>;
				hback-porch     = <46>;
				hfront-porch    = <210>;
				hsync-len       = <20>;
				vback-porch     = <23>;
				vfront-porch    = <22>;
				vsync-len       = <10>;
				clock-frequency = <33000000>;
				hsync-active    = <0>;
				vsync-active    = <0>;
			};
		};
	};

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Tested-by: Dario Binacchi <dariobin@libero.it>
diff --git a/drivers/video/am335x-fb.h b/drivers/video/am335x-fb.h
index ad9b015..c9f92bc 100644
--- a/drivers/video/am335x-fb.h
+++ b/drivers/video/am335x-fb.h
@@ -7,6 +7,8 @@
 #ifndef AM335X_FB_H
 #define AM335X_FB_H
 
+#if !CONFIG_IS_ENABLED(DM_VIDEO)
+
 #define HSVS_CONTROL		BIT(25)	/*
 					 * 0 = lcd_lp and lcd_fp are driven on
 					 * opposite edges of pixel clock than
@@ -68,4 +70,6 @@
 
 int am335xfb_init(struct am335x_lcdpanel *panel);
 
+#endif  /* CONFIG_DM_VIDEO */
+
 #endif  /* AM335X_FB_H */