lcd: add functions to setup up simplefb device tree

simple-framebuffer is a new device tree binding that describes a pre-
configured frame-buffer memory region and its format. The Linux kernel
contains a driver that supports this binding. Implement functions to
create a DT node (or fill in an existing node) with parameters that
describe the framebuffer format that U-Boot is using.

This will be immediately used by the Raspberry Pi board in U-Boot, and
likely will be used by the Samsung ARM ChromeBook support soon too. It
could well be used by many other boards (e.g. Tegra boards with built-in
LCD panels, which aren't yet supported by the Linux kernel).

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
---
v2: Add binding doc, remove ifdefs from lcd.h
ARM: bcm2835: add simplefb DT node during bootz/m

Add a DT simple-framebuffer node to DT when booting the Linux kernel.
This will allow the kernel to inherit the framebuffer configuration from
U-Boot, and display a graphical boot console, and even run a full SW-
rendered X server.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Acked-by: Simon Glass <sjg@chromium.org>
ARM: rpi_b: attempt to turn on power to SD controller

This can't be done yet: The firmware gives an error reponse to
set_power_state. See:
https://github.com/raspberrypi/firmware/issues/106

However, this isn't needed in practice, since the boot firmware must
have turned on the power itself, since it loaded U-Boot from the SD
card.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>