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>