video: fb: vt8500: Convert framebuffer drivers to standardized binding

Now that a display timing binding is available, convert our almost identical
binding to use the standard binding.

This patch converts the vt8500 and wm8505 framebuffer drivers and
associated dts/dtsi files to use the standard binding as defined in
bindings/video/display-timing.txt.

There are two side-effects of making this conversion:

1) The fb node should now be in the board file, rather than the soc file as
the display-timing node is a child of the fb node.

2) We still require a bits per pixel property to initialize the framebuffer
for the different lcd panels. Rather than including this as part of the
display timing, it is moved into the framebuffer node.

I have also taken the opportunity to alphabetise the includes of each
driver to avoid double-ups.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>